Treasure Chest Cavity

So *that's* where you hid the family jewels!

Zoe: You really think there's something in there?
Mal: Using corpses for smuggling is a time-honored repulsive custom.
Jayne: Maybe it's gold.

Zoe: And maybe he was a friend of ours and you need to show more respect.

—Firefly, "The Message"

This trope is about using a person as a walking safe. Or a dead safe, in some cases. Despite the name, the treasure can be hidden in other body parts, and with or without the person's knowledge. Smugglers may willingly have themselves (or others) surgically altered to hide objects inside of them. As shown to the right, in some instances the hidden item may be parked inside the person's Soul or odder "places", as if in a spiritual Hammerspace. Taking the item out may require surgery (hopefully Psychic Surgery to avoid Scars Are Forever), or may be simple if they've been surgically given "pouches".

Examples of Treasure Chest Cavity include:

Anime and Manga

In Bleach, the Hougyoku was hidden inside Rukia's soul.
Inuyasha had his father's grave hidden inside the pupil of his eye.
- Another example; in the very first episode, Kagome had the Shikon No Tama (Sacred Jewel) inside her body. The reason for this is that Kagome is the reincarnation of Kikyo, who, 500 years ago in Feudal Japan, instructed her little sister Kaede to burn the jewel with her body, to avoid any further posession of it.
Hannah from Black Butler II can store inside her things like machine guns, magic swords, and eyeballs with souls. The stored items can be accessed through her bodily orifices.

Film

The Fifth Element. The Stones (the film's MacGuffin) are hidden inside the body of Diva Plavalaguna.
In a rather bizarre version, Christopher Walken's part in Pulp Fiction keeps a pocket watch up his arse to give it to the son of the last owner.
In Underworld the vampire elders Viktor and Amelia had the components for the key to William's tomb surgically placed in their chests.

Literature

Friday. The title character has a pouch implanted behind her belly button that can hold a small object. She often uses it while acting as a courier. At the beginning of the book she's carrying a vitally important message from the Moon to Earth... but, unbeknownst to her, not actually in her pouch, since her enemies know about it.
In Without Remorse by Tom Clancy, part of the plot involves gangsters smuggling drugs from Asia into the US in the bodies of dead soldiers being shipped home from Vietnam.
Labyrinths of Echo had the sword of an ancient King (and in a way, the predecessor of Sir Max) hidden in his chest.
- More specifically, in a magical dream he was stabbed with that sword through the torso and then it "dissolved", leaving him with bloody torn clothes, but no wound - the sword obeys expressed desire (in the 'verse powerful enchanted objects tend to be at least semi-sentient) of its old owner's Shadow to protect its new "hiding place" rather than cause harm. The protection sometimes manifests physically - when Max is struck with instantly lethal magic, it doesn't work, and instead the sword reappears, and can be removed and put back in (the same can be done on request), or dissolves later - but this hurts like... well... having a big sharp piece of metal stuck through the chest. But moving it in and out damages clothes (again, as if the wearer was stabbed in a more traditional fashion). And when Max is hit with mind control, the sword may help him snap out of it with a little sharp pain without reappearing fully. It also occasionally uses Max to fulfill some obligation of its true owner (there's not much after all those years, but it happens). On the upside, it doubles as a magical "keycard" and sort of a wand that remembers some unconventional rituals Max himself cannot comprehend and few people alive know at all, so if his unspoken wishes coincide with the sword's knowledge well enough, Max may suddenly pluck it out and start writing runes in the air with his own blood. All in all, they get along just fine - Max has healthy enough self-preservation instinct to not bemoan a few inconveniences coming with Nigh Invulnerability.

Live Action TV

Doctor Who: In "Dragonfire", the treasure that the "dragon" is guarding turns out to be actually inside its body.
In the Star Trek: Deep Space Nine episode "Who Mourns for Morn?" we learn that Morn stores the latinum from a bank heist he took part in years ago in one of his stomachs, which is why his hair fell out.
In the Firefly episode "The Message", the crew suspects momentarily that the body of their dead friend may have been used to smuggle some sort of valuable cargo. It was, except he ain't dead, and the cargo are artificial vital organs which have replaced his own.
In one season of 24 the McGuffin is a computer chip holding some valuable video, which it turns out was surgically implanted under the skin of one of the terrorists. As he is dying he tells Jack Baur of its location, and Baur cuts it out of him.
In an episode of She Spies, the girls are hunting a thief. As it turns out, what she stole was an experimental artificial heart that she needed to stay alive. An even bigger shocker, her boyfriend was actually a bounty hunter, hired to bring her in and return the heart. At one point, he actually describes it as "an honest-to-God treasure buried in a chest."

Tabletop RPG

One of the most basic uses of fleshcrafting discipline in Vampire: The Masquerade.
- The Samedi can use their clan discipline of Thanatosis to hide or store objects in the folds and wrinkles of their putrid skin. Other vampires can learn this application of the discipline, but without skin that naturally sags and stretches, the results tend to be rather... obvious.
Dungeons & Dragons supplement Deities and Demigods Cyclopedia. The god Druaga was said to store his soul object in a human being. If Druaga's corporeal form is destroyed, the person will die. After the person is buried, the soul object will create a new form for Druaga in the person's grave.
Warhammer 40,000 RPGs have "Concealed Cavity" implant.

Video Games

In Planescape: Torment, the Nameless One can ask several characters to...remove, or otherwise modify, his body parts, like his eyeball, or even his intestines. This results in items being found, and often a stat increase (though it also inflicts significant damage). One specific case involves a previous incarnation storing useful items inside his ribcage, to be found only after finding the requisite clues.
In Morrowind Player Character can come across a quest named “Rabinna's Inner Beauty” in which you have to escort a slave. If you treat her kindly she reveals that her former master hid a portion of moon sugar inside of her to smuggle it to the city and a man you escort her to will kill her to get it out. You can either help her or let her be killed.

Western Animation

Bender of Futurama can hide all kinds of stuff inside his robot body.
On He Man and The Masters of The Universe, Orko would often pull things out of the O on the front of his robe.
In an episode of Jackie Chan Adventures, Jackie unknowingly had the map to a treasure inserted inside one of his dental fillings by a crooked orthodontist.
In a Sherlock Holmes in the 22nd Century episode based upon "The Five Orange Pips", a dangerous weapon is concealed inside the chamber of a man's artificial heart, and Prof. Moriarty seeks to retrieve it. Subverted in that said weapon is by then quite old and worth more as a museum piece than a tool of destruction.
On Xiaolin Showdown, The Yin Jojo (or was it Yan?)^{[please verify]} was hidden inside Dojo's Ear.

Real Life

Truth in Television with drug mules who swallow their illicit cargos or shove them up their rectums in plastic bags to elude searches.
Some politician said once that the launch codes to the nation's nuclear missile silos should be implanted inside an underling's chest, who would have to be killed and cut open to retrieve them. As he put it, the President might think twice about launching the big one and killing untold millions if he had to murder one man with his bare hands and see him lying dead at his feet.
According to QI, a certain pre-industrial travel guide recommended that travelers prepare for potential theft by making an incision in one arm and hiding a jewel inside the wound, then sewing it up and allowing it to heal. Thus one would have some emergency wealth that robbers wouldn't be able to find.