Champions of Far'aus has an In-Universe example with Proctor Henrith Galemore the eleventh, king of Galemore. He is better known as the Popcorn King, because his diet consists mainly of popcorn, and hes almost never seen without a bag of it, which he constantly eats from, and the gold coins that are being minted during his reign have his face on one side, and a piece of popcorn on the other. He even notes himself that he is better known by his nickname.
A handful of these exist in Charby the Vampirate: Charby likes chicken, Mye loves gummy bears, Crispo is obsessed with nachos, Biscut named itself after its favorite food and Breck compulsively shovels down muffins if there are any in front of him. Menu will eat anything.
The Cubi race in Dan and Mab's Furry Adventures scores double. They don't actually need to eat regular food and feed off emotions instead, and each Cubi has a favourite emotion. However, they can eat for pleasure, and typically eat nothing but one or two favourites. Of the main cast:
Fa'Lina seems to have a thing for muffins.
Dan loves ale and according to his sister has eaten almost nothing else in the last three years.
Abel is unusual for a Cubi, in that he eats regularly and eats a range of foods.
Dominic Deegan and "mapvel candies". The threat of said candies no longer being available was enough to trigger a Heroic BSoD.
Dregs: The nudist likes dog food (or "doge chow"). Chub points out that if she was going to be stealing from them anyway, she could have stolen some real food instead. She doesn't care.
In El Goonish Shive, Mrs. Dunkel has been mentioned to bake brownies on multipleoccasions. The Dunkel's seem to like brownies so much that they named their cat "Brownie".
According to his son, Baron Wulfenbach of Girl Genius "really loves waffles."
In Teh Gladiators, guest gladiator Leeroy Jenkins (of World of Warcraft fame) is seldom seen without his crab cakes. Made doubly funny because, in the actual game, crab cakes are a very low level food that would take an entire stack and several minutes to bring a max level character back to full health. True to this, the one time he actually fights on the heroes' side, he doesn't finish eating and get up to attack until after the battle is over. As for the actual Leeroy Jenkins, his food of choice is chicken.
Halo of Grrl Power loves spicy food — so spicy, one restaurant makes her sign a waiver.
Amethyst Lashiec absolutely loves barbeque sauce, such that she'll drink it straight out of the bottle.
Her father, Royce, loves fancy foods in general ("Cuisine" being listed as his muse), but seems to like birthday cakes so much that he not only has one every day, but the theft of said cake is considered grand theft and a capital offense.
In Hyperbole and a Half, Allie's was mistaken for hot sauce for years due to an attempt to impress a family member. She was not pleased by this, especially when she got sets of hot sauce for Christmas instead of toys.
A statistically absurd number of characters in Irregular Webcomic! describe frozen yoghurt as the best thing ever. Curiously, this does not include the resident Big Eater, Professor North Dakota Jones, whose favourite food is "whatever's pricey, yet available in large quantities". With someone else paying.
In Pokey the Penguin, the hero and most other penguins are obsessed with "Arctic Circle candy", which appears to be some sort of plant that only grows in the Arctic Circle.
In Polandball, each country has its stereotypical national dish as a favourite. They're even fond of repeating the names of their favourite food in random background dialogue, or use other countries' favourites as racist slurs. Especially common ones are Turkey with kebab and the USA with burgers.
Ricky from Ratfist loves chili. No, maybe you're not understanding here: Ricky loves chili. He finds a bowl of fresh chili, preparednote almost exactly the way he likes it, in the middle of the street. So he eats it. Bonus points: It was left there by his ex-boss, who mixed in a little cat feces because he needed to infect Ricky with Toxoplamosis gondii.
Schlock is fond of a drink mix called "Ovalkwik." The ingredient list is here.
Ch'Vorthq: Sergeant, you will be drinking a very heavy stimulant cocktail cut with shampoo and high-tensile inert carbon. Schlock: I don't drink it, I eat it straight. Ch'Vorthq: And I suspect you're addicted to it. Schlock:(aims plasgun) Step away from the tub of happiness.
The cast of Schlock Mercenary are also fond of the noble 'Chupaqueso', which is, effectively, melted cheese, wrapped in fried cheese, traditionally garnished with cheese. It's not a good food for a prolonged lifespan, but mercenaries don't tend to live that long anyway.
Gav is a cryo-frozen refugee from the 21st century, and is very fond of Guinness beer. It still exists in the 31st century, but was pretty hard to find. That is, until Gav accidentally cloned himself 950 million times, and suddenly every brewery within a thousand light years wanted to take advantage of the sudden economic opportunity this presented.
Shortpacked!: Robin and anything sugary, given that it catalyzes her Super Speed. Two specific items are more associated with her than others, however: Skittles, which she's often been told she smells like; and Cadbury Cream Egg cerealnote really just Cadbury eggs in a bowl with milk, which gets her so hyper that she blacks out for long stretches of time as she causes increasingly absurd things to happen.