Black Hole Belly

When a creature apparently has the ability to instantly digest anything it eats, allowing it to eat things several times it's size with no change to it's own shape, or swallow living creatures (again, often larger than itself) with no resistance from within. Such a creature can swallow a sword wielding knight or a live velociraptor, but there's no problem since they seem to instantly dissolve the second they enter the stomach.

There are some stories where the characters seem to believe this, and thus make no effort to rescue someone who just got swallowed alive, writing him off the second he goes down the monster's gullet. They probably have at least a few minutes to cut him out before the digestive juices go to work (assuming he didn't just get crushed in the esophagus). Sometimes, they may not even attempt to cut him out after they kill the monster!

Eat the Bomb may depend on this. Compare Hyperactive Metabolism and Nobody Poops. Almost any character with a Black Hole Belly is a Big Eater. Contrast Too Spicy for Yog Sothoth

Anime and Manga

 * Gluttony in Fullmetal Alchemist. Justified as he really does have a pocket dimension in his maw.
 * Similar to Gluttony, Vanilla Ice from Jo Jos Bizarre Adventure uses his Stand to eat anything and everything in its path. The devoured matter is said to enter a dimension that not even he knows where it is.
 * America from Axis Powers Hetalia really should not be able to eat a stack of hamburgers half his height in less than ten seconds, but...

Film

 * Audrey II of Little Shop Of Horrors. Much like Kirby, there's really no place for the bodies to go.
 * Conversed in the song Peth Hai Ya Black Hole (Stomach or Black Hole?) from The Return of Hanuman, describing Maruti being a Big Eater.

Tabletop Games

 * Trolls from Warhammer, thanks to having stomachs full of Hollywood Acid.
 * While most monsters from Dungeons and Dragons do have rules for swallowed creatures fighting their way out, some cause pretty much instant death, from either acid or intense heat. There is also the hellworm, a normal earthworm turned into a demonic Sand Worm by a literal gate to hell conjured inside its maw, which tries to deaden the constant pain by stuffing itself with anything too slow to get out of its way.
 * Magic the Gathering gives us atogs, which can eat machinery, forests, corpses, enchantments, cards in hand, or even time. There's also Atogatog, which eats other atogs. Anything you feed an atog boosts its stats.

Video Games

 * Kirby, of course. Especially since he's about a foot tall. One game actually has usage of his interior as hammerspace as a gameplay mechanic, and it looks like a frikken universe in there.
 * Yoshi can swallow most anything, especially in his original appearance where he can gulp down car-sized Mega Moles. Later games have him process the corpses into eggs, but he can still do it instantly.
 * On the villainous side, there are two: Super Mario RPG gives us Belome, who eats a character, spits him (or her) out, and creates a clone. Before that, or even Yoshi, though, there was Boss Bass, who could swallow even big Mario whole.
 * Pac-Man, naturally.
 * Bow-Wow from The Legend of Zelda Links Awakening, a tiny Chain Chomp who can eat giant carnivorous flowers (and any other enemy in the game) in one bite.

Web Comics

 * Aylee from Sluggy Freelance. People she eats just seem to vanish the minute she swallows them.

Western Animation

 * Nibbler from Futurama, who is even smaller than Kirby . Lrr is a less extreme example.
 * Presumably, Nibbler compresses everything he eats into hyperdense Dark Matter.
 * Rico the psychotic penguin from the The Penguins of Madagascar series. He uses his black hole of a stomach for storage.
 * Shaggy and his canine buddy Scooby Doo manage to do this in some incarnations of the franchise, often with a massive Dagwood Sandwich.
 * Experiment 606, AKA "Holio", from Lilo and Stitch The Series was designed for this to the point where he literally becomes a black hole.