Someday This Will Come in Handy

""You're an absolute gold mine of useless information, you know that?" "There's no such thing as useless information, Kheldar.""

- Silk and Beldin, David Eddings's The Malloreon

Some characters are vast stores of useless knowledge. Now, normally, you'd think that useless knowledge would never come in handy, right?

You'd be wrong.

Because, by Law of Conservation of Detail, or maybe because of some usage of the Idiot Ball, there will rise an exact situation where their trivial knowledge will come to the rescue. Sometimes it requires a Plot Tailored to the Party to happen, other times it just happens naturally. In any case, their so-called "useless knowledge" will save the day. Of course, this is pretty much the mantra of the Crazy Prepared.

This is the subtrope of Chekhov's Gun when the object is something a character knows, though occasionally it is a Deus Ex Machina. May lead to This Is No Time for Knitting. Compare This Looks Like a Job For Aquaman, where it's a useless superpower that comes in handy. When it's a seemingly useless item or knick-knack, It May Help You on Your Quest.

Chekhov's Hobby and Chekhov's Classroom leads to this. Compare Figure It Out Yourself, You Will Know What to Do.

Anime and Manga

 * In Saint Beast, an angel helping Shin move drops a stack of his books and the first one Shin picks up is an old one he's had for a long time about witchcraft transformation. The Monster of the Week? An evil tree that's actually an angel who underwent witchcraft transformation.
 * Back in volume 4 of High School DxD, Sirzechs asks Ise as to what happens if the latter uses Gift on Rias' breasts, then tells him not to worry about it. Seven volumes later,

Comic Books

 * A short Batman: Black And White story by Warren Ellis and Jim Lee features Batman hunting down a murderous senator and fighting his way through his goons. Each skill that Batman uses is followed immediately by a one or two panel flashback showing how he learned it. These include building a remote control, knowing the smell of every aftershave ever, knowing the exact hole size and shape different caliber bullets make in different body parts, kicking a tree in half and identifying how recently someone had a manicure from the nail impressions left in skin.

Film
"Timms: Most of the stuff poetry's about hasn't happened to us yet! Hector: But it will, Timms, it will. And when it does you'll have the antidote ready."
 * This is pretty much the plot of Slumdog Millionaire. Although, it's less that the main character is full of useless information as it is every memorable event in his life happened to intercross with the questions. Sort of like if your life was a Chekhov's Armory.
 * In Planet Terror, Cherry Darling even calls many of her skills 'Useless talents' and numbers them.
 * In Legally Blonde, law student Elle Woods' extensive knowledge of fashion allows her to both a) discredit a witness and b) implicate the true guilty party in the case. And she does it again in the sequel, this time to prove that a certain politician was a) not getting a facial and b) secretly against a "no testing on animals" bill she's working on.
 * In Wayne's World where a security guard conveys suitably detailed explanation about the whereabouts of the big-time music producer Frank Sharp. Wayne hangs a lampshade on it at the time by commenting "For a security guard, he had an awful lot of information, don't you think?"
 * Wayne lampshades this again later, when Sharp's whereabouts suddenly become important: "Aren't you glad we were there to hear that information? Seemed extraneous at the time."
 * The sequel does something similar as well. When Wayne and Garth arrive outside of a studio, a number of men are doing things such as moving a window back and forth across the street, stacking fruit, and so on. When asked why, the workers reply that it's just their job. Of course, later on Wayne crashes through them all in his car in a stereotypical "action sequence", causing the workers to state in satisfied fashion that their job is done. Of course, the "handiness" of this is almost entirely under the Rule of Cool.
 * Monty Python and the Holy Grail. The argument in the beginning about where Arthur's henchman got the coconuts allows Arthur to pass across the bridge over the Bottomless Pit. Sadly, the musical Spamalot used the argument at the beginning, but not the usefulness later.
 * Subverted in Titanic (1997): While being given a tour of the ship, Rose's entourage is shown the equipment in the Titanic's gymnasium, which includes a rowing machine. When offered to give it a try, Rose's mother remarks, "Don't be absurd. I can't imagine a skill I should likely need less!"
 * It probably qualifies more as a Continuity Nod than anything else, but a cut scene in the 1979 sci-fi classic Alien shows Warrant Officer Ellen Ripley reading a bioscanner for crewmember Kane, and failing to understand that he's had an organism planted inside of him. This scene pays off in the third film, when Ripley gets prison staff member Andrews to scan her using her crashed escape pod's bioscanner, and she knows where and how to scan for anomalies.
 * Mindhunters had one character know the exact speed of light, and this came in handy as to figure out how someone would be killed next.
 * Inverted in Paycheck, where Ben Affleck's character is given the (temporary) foreknowledge of his own future, and based on this he gives himself an envelope full of odds and ends that he will need in the near future. However, he gets his memory wiped and must reverse engineer his own future to survive.
 * Charles Morse from The Edge is a collector of useless trivia... some of which comes in very useful when he is stranded in the Arctic.
 * Gloria from White Men Can't Jump collects useless trivia, which comes in handy when she gets onto Jeopardy!. The categories are all her weird topics, like "Foods that start with the letter Q."
 * In Dude, Where's My Car? one of the main characters regularly watches Animal Planet. This eventually comes in handy as he learned that sometimes animals use tools like sticks and also something useful about
 * In My Cousin Vinny, a load of very specific information about old cars comes in handy at the end of the trial. So does Vinny's newly acquired knowledge of how to cook grits.
 * The History Boys plays with this a lot. At least two examples:

"Wilkes: One day it'll save your life. Posner: Nothing saves anyone's life. It just postpones their death. Wilkes: Jesus Christ will save your life, lad, if you'll only let him into your heart. Posner: I'm Jewish, sir."
 * As well as the scene with the evangelical gym teacher.


 * In The Rebound, Sandy's knowledge of sports via fantasy competition is established early. It won't be long till that comes in handy.

Literature

 * Dan Brown's Angels & Demons (as well as The Da Vinci Code) is a particularly Anvilicious user of this trope. In a possible Lampshade Hanging, A&D actually contains the line "He never suspected that later that night, in a country hundreds of miles away, that information would save his life", regarding the fact that one square yard of drag will slow a falling body almost 20%.
 * The page quote comes from either The Malloreon by David and Leigh Eddings. Sure enough, towards the end of The Malloreon something Beldin said turns out to be of vital importance- both the heroes and villains need to find out where to go for the final showdown from the Seers at Kell, when
 * Of course, this is something that Beldin and Belgarath have both known perfectly well for centuries. It's common knowledge among the world's sorcerors and, of course, the Grolims. Mentioning it early in the story for later use is an excellent example of Chekhov's Gun, but this may not exactly fit the trope since it isn't unusual knowledge.
 * The page quote itself simply refers to Silk learning that green is made from blue and yellow...which had absolutely no impact on the plot beyond explaining.
 * Watership Down has a couple instances of this.
 * Early in the book, the rabbits discover that sitting on a floating piece of wood allows a rabbit to float. This is a difficult concept for such simple animals, and only a couple of the group can wrap their heads around it. After using this principle to help a wounded rabbit get across the brook, Blackberry comments: "I admit it was a good idea. Let's remember it. It might come in handy again sometime." And of course,
 * Hazel, on an impulse, saves a mouse from a kestrel. This is seen as unusual because rabbits usually have no associations with other non-predator species. Hazel, however, sees it as an opportunity. Mice are fairly useless to the rabbits, but what would be the benefit of befriending a more useful animal? Enter Kehaar.
 * Not to mention that the mouse later on.
 * Sazed in Mistborn knows a lot about old religions. This may seem useless but
 * Larry Niven lampshades this in his Known Space series. Two of his earlier Known Space stories, "Eye of the Octopus" and "How the Heroes Die" detailed the early manned exploration of Mars, and included trivial data about the planet that wasn't useful at the time. In the novel Protector, set a hundred years later, the trivia about Mars is finally put to use. When asked how the Terrans knew such useless knowledge would one day be useful, Lit Shaeffer says, "No knowledge is really useless... you'll always find some use for it sooner or later."
 * Most of the Fighting Fantasy and Lone Wolf books qualify. Lone Wolf and the Fighting Fantasy series Sorcery, being multi-part series rather than one-offs, are the most worrying with this - certain items might not come in handy for three books. FF at least usually has no rules on how much you can carry. Lone Wolf is not so lenient.
 * In The Pale King, it is randomly revealed that  It comes back in a big way in one of the last chapters.
 * Sherlock Holmes practically defines this trope, what with his knowledge of everything from cigar ash to medical school mnemonics to tattoo techniques.

Live Action TV

 * In Buffy the Vampire Slayer, Xander turns into a soldier during a Halloween episode in season 2. He seems to remember this and the Scoobies use his new found combat skills whenever necessary.
 * On Cheers, Cliff somehow ends up a contestant on Jeopardy!. The clue categories align perfectly with his idiosyncratic "knowledge" (mothers, the Post Office, etc). He dominates the first rounds, amassing a pile of winnings, but of course ends up stupidly blowing it all in Final Jeopardy.
 * On Bones, one of the interns, Mr. Nigel-Murray, spouts off useless facts only vaguely related to the case whenever he gets nervous. Occasionally, his useless facts turn out to be helpful.
 * In an episode of The Good Guys, Jack and Dan track down a criminal to a restaurant because of barbecue sauce left at the crime scene. When Jack asks Dan how he knows which specific restaurant the criminal ate at, Dan responds, "There's three things I know something about: fast cars, fighting crime, and the various good barbecue in the Dallas metroplex."
 * In the Glee episode "A Night of Neglect," the random substitute teacher trivia and later academic decathlon category is "hermaphrodite Nazi sympathizers."
 * Not to mention Brittany, who is anything but bright, helps the team win with her incredible knowledge of cat diseases.
 * Spencer Reid is the king of this trope. Knowledge of Siouxsie and the Banshees, 14th century English literature and government issued traffic reports? You betcha.
 * The "The $99,000 Answer" episode of The Honeymooners. Music-guru Ralph learns he is to be a contestant on a music trivia game show and Norton helps him practice for the show by playing snippets of various songs on the piano. To Ralph's ever-increasing annoyance, Norton always warms up by playing the first two lines of "Old Folks at Home" ("Way down upon the Suwanee River, far far away."). When Ralph confidently appears on the game show, the first musical clue he hears is the same two lines that Norton always warmed up with. Ralph is dumbstruck, can't come up with the answer, and is eliminated from the game on the very first question. For the record, he guessed that Norton composed it.

Tabletop Games

 * All of the gnomes (an entire nation's worth) in the Eberron D&D setting collects information constantly just in case some bit of it comes in handly later.
 * Also in D&D, this is exemplified by the Bardic Knowledge ability, where a Bard might have some random information based on lore he's heard in his travels.
 * In the New World of Darkness Tabletop RPG, Encyclopedic Knowledge, which is a four-dot Merit (keeping in mind that you only get seven dots for Merits at character creation), is basically this, allowing you to make a roll anytime you come across... well, anything, really, that might cause you to remember something you once read/heard/saw that might be pertinent to the situation. Also, you can only buy it at character creation, because "you've either spent your life soaking up useless trivia or you haven't."
 * In the Old World of Darkness setting, a similar effect could be achieved by taking the 5-point "Jack of All Trades" Merit, which basically gave you an "illusory" 1 dot in every Skill and Knowledge, counting as basic training/understanding of each of those abilities. To actually build any of them up required buying the first dot from scratch.

Video Games

 * Done in Banjo-Kazooie. Throughout the castle, you'll come across Gruntilda's (good) sister Brentilda, who will happily tell you all of Gruntilda's embarrassing secrets. Later on, when Grunty challenges you to a quiz style board game, these secrets become your only means to win.
 * Portal 2 (paraphrased)"Moonrocks crushed into powder and then mixed with water"..."makes a great conductor for portals" becomes extremely useful during the final boss battle, not only at the beginning but

Web Original

 * Whateley Universe:
 * Phase is Crazy Prepared enough to pull this off. In the fourth Phase story, he obsesses to teammates about the New Olympians, who might just be incarnations of the real Greek Gods  In the seventh Phase story, the team is trapped in a holographic simulation facing simulacra of... the New Olympians. Phase pulls out his knowledge of them to figure out how to beat Counterpoint and how to rescue Lancer.
 * Phase learning about 'giants' (size Warpers who use a warp field to appear to grow to giant size) in class, and then using that to defeat one in Boston. He also uses the same tactic to defeat the Vindicators in the beginning of Ayla and the Birthday Brawl- he takes over Sizemax's field and uses her like a meteor hammer.
 * Phase is made of this trope, when he's not being Crazy Prepared or the White Prince. There's the lecture he gave on fighting other mutants in "Ayla and the Birthday Brawl". There's the training manual he read in "Ayla and the Great Shoulder Angel Conspiracy". There's the financial expertise he learned about as a child in a super-rich family. There's the knowledge about religious icons he wields in "Ayla and the Grinch". And so on...
 * The Hermit, one of the TAROT villains from the Global Guardians PBEM Universe retains a perfect memory of everything he ever experienced from the time of his childbirth, and is a voracious reader. He's also one of the world's smartest people, allowing him to put his Encyclopedic Knowledge of everything to use against his opponents. He's a villain the heroes hate going up against, simply because he's so annoyingly effective.

Western Animation
"Magnanimous: Now, lose the fight or I'll drop your friends into the quantum singularity! [Flashback to Coop not paying attention at school] Teacher: Mr. Cooplowski! Pay attention! One day you're going to need to know what a quantum singularity is, and then you'll be sorry! Young Coop: Yeah, right. [Back to the present] Coop: Uh, that's bad, right?"
 * Happens twice on Futurama. In one case, Fry's knowledge of 20th-century TV is what saves the Earth from a horde of invading aliens (they wanted to see the final episode of a TV show that was knocked off the air) because Fry spilled beer on the TV station's control panel while delivering a pizza in the 20th century; and in the other case, Fry's knowledge of "good old-fashioned 20th-century garbage-making skills" saves the Earth from...a gigantic ball of 20th century garbage... for now.
 * Subverted in Megas XLR.


 * In Pinky and The Brain, Brain is on a game show, and Pinky annoys him by chatting in his ear. Pinky is about to talk about The Honeymooners when Brain silences him. The final question, worth everything, is about -- The Honeymooners. This is probably a Shout-Out to an episode of The Honeymooners where something similar happens.
 * This trope title comes from the show Dave the Barbarian, in the episode "Termites of Endearment." Dave refuses to practice sword fighting because he's busy making decorative knick-knacks for sale, although nobody wants to buy them. His sister Fang badgers him to practice fighting, and Dave says "trust me, someday my love of decorative knick-knacks will come in handy!" (He keeps saying this throughout the episode, usually directly to the audience.)Then the Monster of the Week attacks, defeats everyone easily, and is about to kill them all—when it notices one of Dave's things and says, "did I ever tell you how much I love decorative knick-knacks?" Cut to Dave selling thousands of knick-knacks to the monster. Fang looks at him and says, deadpan, "I so hate you right now."
 * And his Amazing Penmanship
 * And in another episode, it was his origami skills.
 * And then his pastry baking skills.
 * And Fang's bug-squishing abilities. (Notice a trend?)
 * Teen Titans. Beast Boy's bottomless well of TV trivia knowledge ultimately allows the Titans to defeat Control Freak, who was only dangerous because he also possessed a bottomless well of TV trivia knowledge.
 * Subverted in Rocky and Bullwinkle- in the episode "Banana Formula", Bullwinkle eats a banana on which a secret formula for a powerful explosive was written (don't ask), but thanks to his ability to remember everything he ever ate, he remembers the formula, which is a big help for the bad guys.
 * The Kim Possible episode 'Dimension Twist': Ron's family has just got cable TV and Ron has been glued to it for so long he's memorized the channels. Not something you'd need, right? Wrong. Trapped in TV Land with the hole that dropped him there threatening to undo all of reality, he knew what to switch to plug up the tear in the space/time continuum with a horde of monkeys.
 * In one of Darkwing Duck's origin stories, the phrase "It could come in handy someday," is uttered by:
 * His father, as he gives Darkwing his Omniblaster gas gun (just before his space pod takes off from their exploding home planet)
 * His Quack Fu master, upon completing his training
 * The genie he meets while travelling though the desert, who gives him his costume and his signature smoke-intro
 * There's a Charlie Brown cartoon in which he becomes a spelling bee whiz due to only getting words like "failure".

Real Life

 * Who Wants to be a Millionaire? Since there was no hard time limit until recently, the contestant was always sure to regale the viewers at home with their life story every time they encountered a $200 question that somehow related to it. The first contestant to win the full million (with no lifelines!) was asked which of the options was not a federal holiday. He informed the audience that he was a federal employee and BSed about it for a while before answering the question.
 * Quizbowl. Being a repository of completely random knowledge is an immense asset.
 * Subverted by the canon ( http://www.qbwiki.com/wiki/Canon ), thanks to which experienced players can predict fairly accurately what topics will come up and study accordingly. Probably most of the points good players accumulate are the result of targeted accumulation.