Zombieland/WMG

Buck got sent into the future.
Where he grew up, later joining the UNSC as an ODST.

5 other people will be hired to clean up the zombies.
Salem, Rios, Mattias, Chris, and Jen. Needless to say, it would be done in a day.

This is the early stage of the Green Flu pandemic.

 * Clearly this is the early stage of the same out break from Left 4 Dead
 * Well that would ruin the sequel. "Yay, Talahasse is killing 40 zombies per bullet!!. "RAAAAWWGHHGHHHAWWW" ""Yay, a Tank!""
 * "Oh my lord, Talahasse seems to be beating it to death with a very hard stick!"

In the mansion, Tallahassee states that there are six people left on Earth, when there are only five people present. The sixth person is...

 * Sister Cynthia Knickerbocker, who is some sort of in-universe Memetic Badass.
 * Mickey Knox
 * Whoever is keeping the power plants up and running.
 * Beverly Hills
 * He may believe  is still alive. He seems reluctant to use the term 'died', opting for euphemisms like 'lost' and 'taken'.
 * Well technically, all the "zombies" are still alive, just reduced to virus carriers, like rabies that doesn't kill you. So  is probably a zombie.
 * Chuck Norris
 * No zombie is safe from Chicago Ted!
 * He's speaking in hyperbole.
 * I'm not sure if the scene is on the DVD or not, but when the editor of the film spoke at my school, he showed some scenes where Tallahassee communicates with an On Star employee. It implies they have somewhat of a relationship.
 * Shaun: That is all
 * Does he say that before or after Bill Murray dies? If after the fifth is Sister Cynthia Knickerbocker and the sixth is whoever it was that got the first "Zombie Kill of the Week" mentioned in the movie. There were two.
 * He says it to Bill Murray.
 * The guy with the tuxedo and A.K 47 from the intro.
 * I forget the name, but Bill Murray mentions playing golf with someone, who is presumably alive.

There are safe havens in both the east and west.
Talahasee mentioned conflincting rumors, using that as a reason to write them off. In reality, there are two bastions of civilization left in America. The western one is in Washington, further north than our heroes.

Zombieland happens before Equilibrium, and the 'emotion supressing drug' is actually to supress the virus
The Government of Equilibrium claims that emotions are what the drug is supposed to do, and that they're only promoting peace. But in reality, that's a lie to hide the truth, which is that the drug is to supress the 'virus' that creates the zombies from spreading again, because it can't be cured. They've effectively destroyed all evidence of the zombie plague, and keep humanity ignorant of the truth for what they believe is the best. The lack of emotion is only a horrible side-effect, but one they believe is better than the virus it supresses.

Tallahassee is the originator of Gun Kata
During the big battle at Pacific Playland, while trapped within that prize booth, Tallahassee has a moment of clarity. And during this moment, his body begins to move on its own, performing techniques that will eventually become Gun Kata. After escaping Pacific Playland, he begins practicing and perfecting Gun Kata (then called "Nut Up or Shut Up") and teaches it to Columbus, Wichita, and Little Rock.

They pass it on to others, who pass it on to still others, and it is used to supress the zombies long enough for the supressant to be made. The style is renamed Gun Kata, which is taught to the Grammaton Clerics, and all evidence of its originator is destroyed to hide the zombie apocalypse from the unknowing public.

Zombieism doesn't spread via bites
That's just a myth the characters believe from Wrong Genre Savvy plus circumstantial evidence misleading them. Rather, the mutant mad cow disease was dormant, and had infected most of the meat supply. Anybody who ate beef went zombie over the course of a month or so, people who hadn't eaten tainted beef being increasingly rare due to beef being really popular and people who don't eat it having less muscle mass. This also explains why the girl in the flashback went zombie despite the hobo only trying to bite her. Presumably, nobody has had enough time to let someone confirmably uninfected get bitten and observe them under controlled conditions, and as such they made the logical, if incorrect, assumption.
 * OTOH some people, like Columbus, Wichita and Little Rock are naturally immune to the disease, and won't turn even if bitten directly. Tallahase is just that badass.

There are no zombies
There -were-, but they all died out. Our four protaganists are just murder-crazy.

Columbus's name is Rob Curtis

 * The Hilarious in Hindsight entry on the main page refers to Columbus going "the best thing about Zombieland, no more Facebook updates... 'Rob Curtis is gearing up for the weekend', who cares."

Wichita and Little Rock ran away from an abusive household
Why else would Wichita taker her baby sister away from? It would also explain why they're con girls. Since Wichita was too young to legally get a job, they had to do whatever they could to get the money they needed to survive.
 * Additionally, they're not actually bio-sisters. After all, Wichita, Kansas is about 350 miles from Little Rock, Arkansas as the crow flies, and maybe 500 miles by road. It's much more likely that they are both runaways who met on the streets and became partners in crime for their mutual protection.
 * To the first, they could be orphans instead. To the second, but keeping with the abuse, they could have lived with one parent each, one in Little Rock, one in Wichita.

Tallahasee is Mickey Knox
Somewhere between the end of NBK and Zombieland, he had a falling out with Mallory, moved away and had his tattoos removed. This explains his natural zombie-killing ability, he's had a lot of practice. The reason that he never tries to murder anyone living is that the world no longer disgusts him, and his aggression is easily gotten out on Zombies.

Tallahassee is T. Sean Collins
Before he met up with Columbus, Tallahassee worked for a short time protecting celebrities from zombies in a man made fortress. After escaping the failure of said fortress, he stole one of the celebrities' Cadillacs out front and drove off, modifying it with a plow and the trademark Earnhardt 3 as he went along.

Tallahassee knows something we don't
The sixth person he's referring to is another survivor he met but parted ways with. He never mentions them except by accident because they didn't leave on good terms. It's likely that whoever it was was even more insane than the girls and would rather be holed up in a compound somewhere where they know they're safe rather than have another survivor for company. Or maybe they just thought his quest for Twinkies was dumb.

Tallahassee wanted to die, but on his own terms.
When he reveals that his son was killed by zombies, he says something to the effect of, "When you take a man's son, he doesn't have anything else to live for." However, he is too proud for suicide, and wants to die in such a way that it will take out as many of those living-impaired bastards as possible. Therefore, he leaps into battle with both guns blazing, knowing that any fight may be his last, but that's fine because he will take down fifty or a hundred zombies before they tear him apart. However, meeting Columbus and the girls ended up having a similar effect on him as it did on Columbus; he has a family now, and therefore something to live for.

Zombieland is the sequel to Adventureland.
This is a rather popular theory
 * Then there's the accompanying sub-theory is that Columbus is James Brennan.
 * I like the idea, but he lived in Pittsburgh, not Columbus - unless his parents had moved due to his father's drinking issues. But then how did he get to the university in Texas?

Buck is still alive.
Tallahassee mentions six people, one more person that there should be. Some say he's in denial about his son, Buck, being dead. But I say that denial is actually true, and his son is now a ten year old badass who's second only to his father at killing zombies.
 * While Tallahassee is master of the head-on, More Dakka assault, Buck's small size and low ammunition carry-weight led him to perfect the art of anti-zombie guerilla tactics.

Zombieland is in continuity with Dawn of the Dead 2004.
No justification, I just think it would fit nicely.

Zombieland 2 features replacement protagonists.
Because the end of Zombieland pretty much cemented the formation of True Companions, and there's probably not much else for them to do but Walk the Earth and kill zombies, maybe stumble onto a safehaven in the process, which would end the story. Two possibilities: I take back my initial statement because there's one thread still hanging - whether Columbus' family is alive. If "people out west hear it's the east" and vice versa, then maybe Wichita's news wasn't that reliable. Zombieland 2: Road to Columbus.
 * An actual family's POV, beginning with a literal Shoot the Dog moment, then leading to a roadtrip to Grandma's place, where the family minivan is slowly turned into a Weaponized Car in the process. Expect Mommy to skillet (rule #6) zombies left and right with Baby strapped on. This family probably originates from the town where the zombie princesses appeared (little Bonnie was spared cos she had pinkeye that day).
 * Alternatively, a group of soldiers' POV. After touring Iraq, The Squad is finally sent back home when they learn they'll be needed for some nasty business back home - cue the plane crashing when their pilot turns out infected. Basically these soldiers were responsible for leaving that tank in the street that Columbus and Tallahassee walked by, and the yellow humvee was only there because it was too obvious a target (they took two darker colored vehicles and maybe just 2 or 3 guns per soldier).
 * Sorry to say, but Jossed by recent Word of God, in an interview with io9. Well, semi-Jossed. It will have a new group of survivors, but they tag along with Columbis and the gang.

Zombie Kill Of The Week...
If they went with a tv series instead, was it meant to be a recap from the ep itself, or some funny outtake, or even better, either at random? God forbid they go with 3. viewer submissions...

The Zombie plague happened in October 2008, before World of Warcraft's Wrath of the Lich King Expansion
That's why as he was playing World of Warcraft, he thought nothing of the people typing "I'm under attack by zombies! Help!" in the trade and guild channels.

Columbus is actually Mark Zuckerberg
Someone had to suggest it.
 * So The Social Network takes place in the past, and is Columbus's backstory? And what happened to Eduardo?
 * Eduardo is a Zombie.
 * The best thing about Zombieland? No more Facebook status updates.

Wichita never intended to get out of Pacific Playland alive
She only wanted to show Little Rock a really good time, one last day to be a kid, before shooting her, and then killing herself. This would expand on Wichita's general cynical worldview, and her decision not to stay with Columbus at the mansion and instead go ahead with her original plans. It also turns a wallbanger (How could she think turning on the lights and sounds in the whole park would not attract zombies?) into a more reasonable action (one last desperate ploy for happiness, before inevitable death) and rather intensifies the happy ending (Not only does she choose to be with Columbus, she chooses life!). Also, it would have been a really cool twist, although, admittedly, incredibly depressing. "Happy, sis?" "Yeah!" "Have a good time?" "Yeah! The best time ever!" "I'm glad." BANG!
 * This is now canon in this troper's mind.
 * This is not without precedent: though without zombies, the "give the person you love happiness before you mercy-kill them" forms the end of the novel.

They're in the same universe as Planet Terror
Rather Garland Texas where it started was the small town from Planet Terror and the story of Mad Cow Disease was just a government cover up. So if they do go to Mexico like Tallahassee wanted they'll meet up with Cherry and Dakota Block.
 * Not that I wouldn't love to see this crossover, but the zombies in the two universes are very, very different...

Tallahassee is Chicago Ted.
He stayed in Chicago for a while under his real name, Ted, and began racking up more zombie kills than anyone ever thought possible. Word of his zombie-killing skills spread across the nation, cementing him as an in-universe Memetic Badass. Then Chicago became too overrun even for him to handle, and he fled and started going by Tallahassee.

Cine-A-Sorrow Theater shares a universe with Zombieland.
Let's look at the facts--it's been confirmed that CORPS has been eliminated, leaving no resistance fighters in either 'verse, and if the population has dwindled as much as is shown in Zombieland than the idea of hordes of zombies hanging around outside the theater waiting for the two humans inside to come out actually makes sense.

If a Zombie bites Tallahassee, he will turn into Tallahassee.
Admit it. You think it's an awesome theory.

Zombieland takes place in the same universe as the Twenty Eight Days Later series.
1. Both have fast zombies caused by a virus.

2. Even though Columbus says it was Mad Cow Disease, it could have been the Rage Virus - he also says that it made people "hateful and violent."

3. Boom! Headshot! is not necessary to kill the zombies in both universes - both movies specifically say that the "infected" are not dead, just driven insane by the virus and its symptoms. (Which is why a bat works in both universes.) Also, they have an alarming tendency to spew fluids over anyone within spitting distance - when they aren't taking you apart. And they are smarter than the old fashioned shambling variety zombie - again, because they aren't dead and have most of their faculties.

4. Survivors in both universes take comfort in sugary treats - Twinkies (and Snowballs) in the Zombieland universe; in the 28DaysLater 'verse, it's Chocolate Oranges.

However, the moment when Selena (in Twenty Eight Days Later) says "if I never see another chocolate bar again, it will be too soon", bad things start to happen to everyone. The folks in Zombieland never make that mistake.

(Rule 33 of Zombieland - Never diss The Power Of Chocolate.)

5. Candy is dandy, but liquor is quicker - Frank and Tallahasee both know the good stuff when they see it.

Zombieland and Twenty Eight Days Later are really the same story, but told by different groups of survivors.
Think of the original tale being passed down by survivors in different places, and the story gets changed to suit its audience. Which is why both stories feature:

1. Rumors about places free from infection.

2. A long road trip to get to the "promised land".

3. Sugary goodness.

4. Baseball bats.

5. Liquor.

6. Two females and two males - one older, one younger. And two of them are related.