In the Jackie Chan Adventures fic Queen of All Oni, after Jade becomes a Shadowkhan girl once more, her appetite and metabolism greatly increased, to the point that, in one chapter, she is described as eating a rib, BONE AND ALL, and has eaten large amounts in several other chapters (to be fair, she did have a big appetite BEFORE the transformation, as Season 2 episode 9 shows).
In Seth In The Pokecity, we have Seth himself. While it's mostly a Sweet Tooth, he has no qualms about eating ample-sized amounts of things like pizza or ramen, either.
John in With Strings Attached. Eats at least three times what a normal person eats. He can ingest and draw nutrients from just about any organic substance. As a side effect, he's immune to poison and drugs, including alcohol.
Agumon was always a big eater, but in Transcendence: Digital Curse he consumes enormous amounts at some times. At one point he manages to eat a dozen or so containers of food, and he keeps eating an unspecified amount more. Justified in that case.
Haruhi, Kuyou, and Tsuruya in You Got HaruhiRolled!. The latter is implied to be able to devour at least ten times her own body weight.
Kit from the Hunger Games fanfic Some Semblance of Meaning is a Mouthy Kid in more ways than one. When asked what his favorite food is, he responds, "Everything!" And the narrative once described him as "eagerly attempting to gobble down half of the Capitol's food supply" at breakfast.
Simba eats way too much food at King Hapana's pride in Desperate Measures, developing a Balloon Belly in the process. It turns out that King Hapana was deliberately fattening him up in order to slow him down so he couldn't escape.
Haiba eats so much at Jowai Resort in Changes that he becomes morbidly obese. It also spawns his alter ego, Don Haiba.
In both cases, the obesity wears away by the next story.
One case where it's not played for laughs is with Raven (not this one) in Yu-Gi-Oh, The Thousand Year Door: Redux. Having grown up among the impoverished underclass of Madripoor, where the rich are usually content to let the poor starve, she learned quickly to take as much food as she could and eat it as fast as possible. Even though she managed to escape the oppressive society, she still has her old habits, and wolfs down her food at the pre-finals banquet.
The Twilight Child: Scootaloo manages to win an eating contest against already established Big Eater Pinkie Pie, as well as Rainbow Dash and Trixie.
Princess Celestia, as well. At Twilight Sparkle's birthday party a character notices her casually chowing on an extremely large wedge of cake, to the horror of the Canterlot ponies watching.
In Pet Me, Damnit!, one of the traits Harry Dresden retains while shapeshifted into a dog is his perpetual appetite. Hendricks describes him as a "living vacuum cleaner."
In Pokémon Reset Bloodlines, Ash and Misty routinely eat enormous quantities of food. This is because they're bloodliners, and like most bloodliners, they have higher metabolisms than normal humans.
Anime Crossover Tournament has a few:
The battle between the team from Slayers (the protagonists) and the one from Dragon Ball ends in an eating contest between Lina and Goku. Lina wins-and between the two they made the cooks work so much they went on strike.
Gourry proves his mettle in the third chapter, as due the cooks' strike he couldn't eat at the arena and was wandering moaning "Food" until he stumbled on the defeated Hamtaro team. At which point he finally had a small snack.
Usagi shows herself one, gorging on the five free servings available to each competitors after the cooks' strike ended... And getting furious when Lina and Gourry barged in and ate all the food. Because they're on a whole different level of Big Eaters, and five servings weren't enough for them.
In the Kim Possible fic The Ronless Factor, when the crisis concludes with Ron being brought back from the dead, Tara blows a months shopping budget to give Ron a big enough meal to celebrate his resurrection.
Both Link and his daughter Neolani from the Legend of Zelda fic Offspring eat a lot. Neolani is still hungry after eating two fish, while her sister Mira can only eat one.
Black Alice in The Tyrant and the Hero. She's capable of eating an entire deer and thinks of pigs as "bite-sized". Heinrich is actually able to tell that she's unsettled when she eats a normal amount of food.
The ability to put away absurd amounts of food is a quirk of Selina Kyle in the Dusk to DawnBatman fan novels. She's always on the lookout for something to eat, even in the middle of a brawl, and a sure way to piss her off is get between her and a meal. Of course, it's less funny when you realize the instinct to scavenge is from her chronically hungry childhood as a Street Urchin.
In Amazing Fantasy, Inko is concerned when Izuku starts scarfing down plate after plate of food for breakfast when he used to barely touch his food before the spider bite. After finishing everything she gave him, he then proceeds to gobble up the leftover eggs in the pan with a piece of toast.
To Hell and Back (Arrowverse) has Barry, Kara, and Kal gobbling up huge quantities of food at every possible opportunity, much to Oliver's simultaneous disgust and resignation.
Shaggy the Handler deconstructs Shaggy's appetite. He eats so much because, while serving in Vietnam, he was left on his own for a week and almost starved. He doesn't want to feel that hunger ever again.
Let Us Be Your Poison: Pyrrha eats large meals because being a Huntress requires a lot of energy. For example, her breakfast in chapter 24 consists of 5 omelets, 12 strips of bacon, 6 links of maple sausage, 4 slices of tomato, 8 pieces of toast with butter and jam, and a very large glass of orange juice.
Hohenheim in My Master Ed has the same voracious appetite as Edward. In his case, this is at least partially due to his backstory of being a slave and never before having the amount or variety as he does after being freed.
Deconstructed in Arcanum. Having lived in poverty for entire life, Ruby got used to eating as much as she possibly can for fear of going hungry later. Once she is presented with an abundance of food, she not only wirds everybody out with her absurd appetite, but also gets sick and ends up vomiting out most of said food.
In To Catch A Raven, Raven explains to her girlfriend that she eats one small meal a day. Once a month, she consumes a large amount of of meat. It's related to her being half-demon.
He ate a omelette and toast with english muffins and he had bagels and Cap'n Crunch. He was also eating orange juice a muffin and sausage and a bacon piece but he also ate just bread.
In A Load Of Bulk, Lana Loud from The Loud House drinks a strength potion and one side effect is that she ends up extra hungry, raiding the fridge a lot and having 50% more breakfast than usual.
Unbreakable Red Silken Thread: Shawn mentions in Chapter 26 that he would eat a large pizza on his own if Cody and Cameron took longer than planned during Cam's driving lessons.
Fate/Black Dawn: In canon, Arturia would eat platefuls of Shirou's cooking and demand more. Shirou assumed it was a result of her being a Servant and needing lots of food to keep up her mana supply. When he meets her sister Morgan and child Mordred, he's mildly annoyed to discover that no, the entire family can eat their own body weight in food in a single sitting. And since he's apparently the best chef in Britain, they won't eat anyone else's cooking.
Bucky Barnes realizes that as a result of Zola's knockoff Super Serum, he should be eating somewhere around 9000 calories a day. He's so mentally disorganized he has to set reminders to eat, but once he gets that squared away, his hallucinations largely stop and he starts really bulking up, to the point of being almost unrecognizable compared to how he looked in DC.
Steve Rogers is no slouch in this department, either, having gotten the real serum. His caloric requirements are almost to Blessed with Suck levels for him because he's more susceptible to starvation and malnutrition than a baseline human- it was found during the war that he can go almost 72 hours on almost no food, but after that, he'll go into a state of lethargy where he basically falls asleep on his feet.
"Back on the farm, before she got her cutie mark, Pinkie barely ate four muffins a day. Afterwards however, she couldn't seem to get enough food in her! It's one of the reasons she moved away."
The Heroic Chronicles of a Young Man: Tenya Deguchiya comes from an entire family of big eaters on his mother's side due to their quirks. Said quirks range from porcine mutant quirks to producing metal from their body to firing laser beams. Pretty much all of them put away several plates worth of food every meal, and they encourage Tenya to marry Momo specifically because she also has an eating based quirk.
Casey believes that this is a side effect of an active Aura in Boldores and Boomsticks after seeing how much both Team RWBY and their Pokémon eat. This is confirmed after her Aura is unlocked and she barely feels full after eating five sandwiches.
A Moon and World Apart: Celestia, at least when it comes to cake — as Luna informs Cadance in chapter 28, Celestia once dove into an Olympic-size swimming pool full of cake and devoured it all.
In A Very Potter Musical, Ron Weasley always has a snack, including but not limited to: a carton of Chinese food, a bag of Funions, Twizzlers handed to him by a member of the band, and a Hershey bar the size of his torso.
Ron: Accio double-stuffed!
Wheatley becomes this after GLaDOS implants his brain into a human body in the Portal 2 fic Test of Humanity. He ends up eating everything in Chell's fridge after tasting food for the first time, and, later on, GLaDOS tricks him into eating 30 cakes. By the end of the fic, he's grown noticeably fatter.
The sequel has Chell's roomates being unable to make anything for dinner because Wheatley already ate nearly everything. And, Wheatley then admits he made a large order for Chinese takeout...most of it being for him to eat.
Mike gets away with being called fat in Pokéumans - as a Ditto he resembles a pink fleshy blob and turns into a Munchlax so he can eat more.
Choji in the Naruto fanfic Kitsune no Ken: Fist of the Fox, just like his canon counterpart. At one point, Sasuke actually takes advantage of this to convince him to fight Shikamaru during the qualifying round of his tournament—in addition to getting tickets for the upcoming Shadow Fox comic-book movie, they're told that there'll also be a buffet line, as the screening they'll get to see is that which is usually reserved for movie critics. Choji immediately jumps on board.
Yajirobe's appetite is played up in Dragon Ball Z Abridged, most notably with an FAQ video where he apparently started eating Yamcha's body and Bulma correctly fearing he might eat Trunks out of spite and/or hunger.
The Chandlers (though the only fat one is the titular Chris) in Christian Potter Chandler. Bob eats breakfast at Burger King every day and brings home a 4-person meal for his family of 3.
The Bolt Chronicles: Pennys mom becomes this in The Baseball Game, much to her daughters embarrassment. As a guest of honor, she takes full advantage of an offer of unlimited food and has three hot dogs, two bacon cheeseburgers, two chili cheese fries, a bag of peanuts, a bag of popcorn, cotton candy, two boxes of Cracker Jacks, a jumbo sausage with peppers and onions, two pretzels, a nacho plate, a couple corn dogs, a soft serve sundae in a souvenir batting helmet — and a diet soda.
Alex Mack's powers are Cast from Calories in The Secret Return of Alex Mack, causing her to regularly eat several times as much as a regular person. If she's in public, she'll usually eat a normal meal, then have a second one in private, and her missions always end with her team leader providing food. On the bright side, her supercharged metabolism means she basically can't become overweight.