Security Blanket

I need my blanket! I admit it! Look at all of you! Who among you doesn't have an insecurity? Who among you doesn't depend on someone, or something, to get through the day? Who among you can cast the first stone? How about you, Sally? You with your endless "Sweet Babboos"? Or you, Schroeder? You with your Beethoven, Beethoven, Beethoven?! And you, Lucy, never leaving Schroeder alone, obsessing over someone who doesn't care if he ever sees you again? What do you want?! Do you want to see me unhappy? Do you want to see me insecure? Do you want to see me end up like Charlie Brown?! Even your crazy dog, Charlie Brown. Suppertime, suppertime, suppertime! Nothing but suppertime 24 hours a day! ARE ANY OF YOU SECURE?!

—Linus van Pelt, Happiness is a Warm Blanket, Charlie Brown

As defined on The Other Wiki "A security blanket is any familiar object whose presence provides comfort or security to its owner, such as the literal blankets often favored by small children."

When you deal with small children, it is a common sight to see them carrying something such as a blanket or stuffed toy. In fact, some children are attached to this object to the point of making it a Companion Cube. There are numerous reasons for this, but the simplest and most common is the fact that, as the definition above says, it provides comfort to the owner.

While blankets are perhaps most common, the Security Blanket can be any object. A toy, a pillow, some kind of trinket. Can also be a type of Magic Feather, giving its owner a bit of confidence where otherwise they would have none.

If the character is separated from their Security Blanket, or it is otherwise destroyed before they're ready to let go, expect the crying and Inelegant Blubbering to commence ad nauseum. Especially, in Real Life.

The Other Wiki calls this a "comfort object".

Can overlap with Girls Love Stuffed Animals. Compare Living Emotional Crutch or Overwhelming Obsession.

May be a Number One Dime.

The Trope Namer is, of course, Linus' blanket in Peanuts.

Examples of Security Blanket include:

Advertising

Chef Boyardee: Abby and Bridget still have their Blankies, despite trying to pretend they don't. According to Abby's blanket, she is acting like she is too old to have a Blankie but not for Boyardee Ravioli.

Anime and Manga

Nodoka from Saki can't sleep without her stuffed penguin, Etopen. She's also encouraged to hug it when she plays Mahjong with other people, just as she does online, with the hope of improving her skill.
Asuka Langley Shikinami is awfully attached to her little red doll in Rebuild of Evangelion...
- Which is eiher ironic or creepy when you recall how Asuka Langley Soryu felt about dolls in the original series.
Sawyer throws a fit and then goes unresponsive in Black Lagoon when she loses her Ultravoice.
Kiri Komori's blanket in Sayonara Zetsubou Sensei. The episode where she loses it references Linus.
A bit twisted in Berserk, since Guts's security blanket is his Blade of Fearsome Size. He says that he's more at ease when he has it on hand and has a hard time sleeping without it of course, he had a very nice time sleeping without it when he was with Casca....
Subverted in Black Butler. Ciel says he can't sleep without his preferred pillow, but it was just an excuse to hide the blood on Sebastian's chest.
Erio Towa, the Hikikomori main character of Denpa Onna to Seishun Otoko finds it difficult to interact with people without having herself wrapped securely in a futon. Even after getting over the worst of this she finds it soothing.
Yumekui Merry's Merry Nightmare panics when she misplaces her Nice Hat.

Fan Works

In Progress, a My Little Pony: Friendship Is Magic fanfic, Luna has a security abacus.

Film

Leo Bloom in The Producers always had a small piece of his blue blankie in his jacket pocket.
Blazing Saddles:

Hedley Lamarr: Where's my froggy?! Where's my froggy?!
Daddy loves froggy. Froggy love daddy?

In Buffy the Vampire Slayer, Buffy has a small teddy bear that she cuddles for comfort at night following her nightmares of past incarnations.
In Best in Show, one of the contestants in the dog show is extremely high-strung (like her owners) and can't function without a specific toy called a "Busy Bee."
In L: Change the World, Maki has a pink teddy bear that provides comfort for her when ever she's in distress.

Literature

In Discworld, blankets are the primary form of defense against bogeymen. You can either put it over your own head so they won’t notice you, or put it over their head to make them think they don’t exist.
- Not a blanket, but Esk in Equal Rites finds comfort in having her wizard’s staff close at hand, even when it’s disguised as a broom and isn’t doing anything to help her.
In The Hitchhiker's Guide to the Galaxy, it is important to know where your multi‐purpose towel is. At all times.
In The Egypt Game, Marshall carries around a stuffed octopus called Security.
In Robert A. Heinlein’s Have Space Suit—Will Travel, Peewee admits she can’t sleep at night without her doll Madame Pompadour, even as she admits, “I’m perfectly aware that it’s just a doll; I’ve understood the pathetic fallacy for — oh, years and years!”
Jane Eyre’s childhood attachment to her doll makes this trope Older Than Radio:

“It puzzles me now to remember with what absurd sincerity I doted on this little toy, half fancying it alive and capable of sensation. I could not sleep unless it was folded in my night‐gown; and when it lay there safe and warm, I was comparatively happy, believing it to be happy likewise.”

In a way, the six‐fingered man’s sword serves this function for Inigo in The Princess Bride (not in the movie so much). He’s really rather lost without it. This has more meaning than many examples of the trope, since his father made it and was killed over its worth.

Live Action TV

Stephanie Tanner from Full House had Mr. Bear. Even after the character outgrew carrying the toy it remained a common sight in her bedroom.
Buffy the Vampire Slayer: Buffy's Security Blanket is apparently her favorite stake, Mr. Pointy.

"I guess I don't really have a security blanket...unless you count Mr. Pointy."

This stake was originally the favored stake of Buffy's fellow Slayer, Kendra, who gave it the name.

Finn seemed to have one of these in Glee which he called his "gee gee."
On Gilligan's Island, Mr. Howell sleeps with a teddy bear, the fact that he needs it being one of his most visible weaknesses.
In M*A*S*H, Radar slept with a teddy bear (likely to symbolize his childlike innocence) which he was always a little embarrassed about. However, in the episode where he left the cast (where his going-away party was cancelled due to an emergency rush of wounded shipped in and he had to leave without saying goodbye to anyone) he leaves it behind so they can remember him; Hawkeye and the others find it in the last scene. In the Grand Finale of the series, it is one of the objects they place in the time capsule.

Newspaper Comics

Linus and his blue blanket from Peanuts are perhaps the most famous example, and also the Trope Namer as The Other Wiki credits the series for the term "security blanket." Schulz claimed he based the idea on blankets his own daughters had when they were children, and had no idea the term would become so popular.
Another comic strip example: when Baby Blues' oldest child was a baby, she was inseparable from her "Boo-Boo Bankie".
When Doc Boy visits John in a Garfield story arc, it's revealed he hasn't been able to sleep until his mother gives him his old blanket.
- Also, Garfield has Pookie.
Calvin has Hobbes, of course. This aspect of their relationship is showcased most clearly in the series of strips in which Calvin and his parents go to a wedding and come home to find their house has been robbed.

Theater

The plot in Cirque Du Soleil's Mystere kicks off when two babies (played by adults) lose their loveys—a big red ball for the male, a toy snail for the female—and venture out into the world to find them.

Video Games

Sunday from Cla Dun is extremely shy and paranoid around others. The only thing that truly gives her comfort is her sword.
One of the items of Vendor Trash a hero can acquire and then sell in Godville is a High-Security Blanket.

Western Animation

Buttercup needed one in The Powerpuff Girls episode, "Cover Up." Eventually she was convinced to let it go and passed it to Professor Utonium. Also, Bubbles consistently has Octi, who sometimes gets the Companion Cube treatment, a fact taken advantage of by HIM in one episode.
In Rugrats, Angelica's ratty old doll Cynthia is her security blanket. She goes ballistic when the babies lose it.
Franklin, the turtle in the books and TV series by the same, had a blue one. At one time, he took it everywhere with him, though eventually he only slept with it. Late in the series, in Back to School With Franklin, he gave it to his little sister, Harriet, who later lent it to Beaver's little brother, Kit.
Cow from Cow and Chicken had one in "Cow's Magic Blanket" until Chicken lets the other kids know and they mock her for this, resulting in Cow throwing it away. Then she tells Chicken that blanket was Supercow's source of power and that, without it, there's no Supercow. Upon overhearing this, Red Guy started hurting the other kids, until Chicken rescued the blanket.
Cassie's little brother Finn has one in Dragon Tales.
Deedee from Dexter's Laboratory has a teddy bear named Foozeems. When Dexter throws it away, Deedee has an Angst Coma of sorts in which she acts like a zombie and repeats "Foozeems, Foozeems, Foozeems" all over, so Dexter has to go on a quest to retrieve it.
Family Guy; Stewie has a teddy bear named Rupert who he feels is the only, er, person he loves more than Brian. In one episode, after Brian accidentally destroys Rupert in a drunken stupor, Stewie's grief and anger towards Brian seems like overreacting. When Brian inquires how Stewie - who is unquestionably the smartest infant in the world - could depend so much upon a teddy bear, Stewie gives it to him straight: no matter how rich and successful he becomes, Brian and Rupert will likely be his only friends, and more likely than not, he'll outlive Brian.
In Bob's Burgers, this seems to be the reason for Louise's pink bunny-ear hood that she always wears. She tends to freak out if she's in danger of losing it.

Web Comics

Susan in El Goonish Shive is known to wear Star Trek shirts whenever she's upset about something, which Elliot directly compares to Linus and his blanket. Though Sarah would never dare use that analogy around her.
- Tedd's glasses are also mentioned as being used for this purpose.
In Strays, Meela's brother brought her stuffed bear from home. She clutches it but is less than consoled, given the extent of trauma she's been through.

Real Life

Plenty of instances to make this Truth in Television. This troper's youngest niece is the reason he mentions pillows in the description.
As noted above, "security blanket" originated with Peanuts; insurance companies quickly adopted the term.
Project Linus also took the idea and ran with it. Volunteers with this non-profit organization sew, knit, crochet, and quilt security blankets for children and teenagers who are hospitalized or suffer other traumatic experiences.
Actually, quite a large number of people actually have a great number of rather mundane items they would be uncomfortable going through their day without, (pants, shoes, wallet, etc...) but these items are so common, its hard to see them as "Security Blanket", until yours are missing and feel the panic...
There actually are items that some people with a medical condition can’t be without in case something goes wrong. For example, someone with a seizure disorder would see their alert bracelet as a security blanket because that would let a bystander know what is wrong and get medical help.