Surprisingly enough, while I'm not a cooking enthusiast I still managed to pepper my stories with little details about my agents' food preferences.
It may sound stereotypical Italian for Sergio, but his favourite dish is the most iconic Italian food of all: pizza. He's quite picky on how it is prepared, though, and there are some toppings that should never be mentioned as such in his presence: pineapples, of course, but also anchovies get a hard no from him. In fact, I dare say he usually goes for the bare minimum: tomato sauce, mozzarella cheese and either a couple basil leaves or a sprinkle of oregano depending on what is available.
In general, he tend to stick to Italian cuisine (which is also what he cooks himself) but he appreciates Japanese cuisine too.
As far as beverages go, he tends to stay away from alcohol (and dosn't actually have much of a tolerance for it in the first place) and he is on "team red" on the eternal CocaCola VS Pepsi debate (though he doesn't really argue on Coke being better, he just prefers it).
Nikki's tastes, as a badfic clone of Sakura Kinomoto, still tend to stick closer to her original to this day - with some notable differences, though. While Nikki still loves rice omelets and fried noodles (Sakura's favourites), her favourite dish is actually okonomyaki which as far as I remember wasn't actually mentioned as being something Sakura likes. As far as cooking goes, she tends to be more confortable preparing Japanese dishes, but she appreciates eating Italian cuisine too.
She still uses the very same pancake recipe Sakura uses, though, with which she has become very proficient - at the cafè she worked after retiring from the PPC (and before the Unravel in the relevant timeline) the pancakes she made were hot sellers.
Interestingly enough, sweets-wise she has a bit of an inversion compared to Sakura - if the TWWA equivalent of the Cardcaptor Sakura: Clear Card chapter revolving around macarons happened with her present, she was amused by the fact she prefers lemon-flavoured ones over chocomint ones while Sakura is the opposite. Something that extends to their boyfriends, too - Syaoran prefers lemon, while Sergio... actually doesn't like macarons at all, but in general he prefers chocomint over lemon in sweets.
This inversion compared to Sergio extends to soft drinks as well - Nikki prefers Pepsi. On the alchol front they're the same though - Nikki isn't a fan of liquors, wines or beers either, and she arguably handles alcohol even worse than Sergio does.
Corolla's favourite dish is more of a tricky question. Before Blank Sprite, it was the infamous Sue Soufflé, but she found herself unable to eat that dish anymore after discovering Sergio used to be a Suvian himself. CAFfine is still fair game to her though (by the way, that stuff seems to have completely disppeared from the Wiki - why is that?). Food-wise, though, I don't think she currently has a true favourite, but she has quite the sweet tooth so it would be definitely some kind of confectionery.
She doesn't know how to cook, and she isn't even interested in learning - that's time better spent tinkering with stuff!
Keiko's favourite dish, as mentioned in her very first mission, is lasagne (with extra besciamella sauce). That aside, she appreciates both italian and Japanese cuisine equally (having experienced both thanks to her parents, as they take turns cooking), but isn't really a fan of overly sweet stuff - she's more likely to have salty snacks over sweet ones (with a few exceptions, liek azuki bean flavored KitKats) and as far as soft drinks go, she prefers the somewhat bitter chinotto over both Coke and Pepsi. Being currently sixteen she never really had much in the way of alcohol yet (so far having been granted an exception in the Unraveled World during the podium celebration of her debut Cyber Formula race), but she suspect she isn't going to be much better than her parents in handling it.
She tried her hand at cooking from time to time, but by her own admission she's quite average at that.