A good portion of the food in ROTN (Rebirth of the Night) is from the HarvestCraft modpack - a wiki for those recipes and more can be found here. However, there are still several ways to craft comestibles outside of that modpack, separate from vanilla cooking.
In ROTN, many mobs drop some sort of flesh that can be cooked and consumed. To start, Hungry Zombies and Hungry Spiders have a chance to drop vanilla foods upon death. If you're looking for wings, bats and petras (flying green dinosaurs) drop their respective wings that can be cooked for slightly more saturation. Parasites from gravel or zombies can drop themselves upon death, and can then be cooked to fill half a nugget. Finally, bee grubs can be harvested from working apiaries for cooking and consumption. It should be noted that in HarvestCraft recipes where any meat is accepted, bee grubs and bat wings are accepted.
Getting food in the beginning of the game is mainly based around fruit collection. Despite the fact that ROTN uses Biomes O' Plenty, the once harmless berry bushes have been replaced with Hawthorn bushes, spiky plants that give bitter Hawthorn berries. While hawthorns are desired by animals (specifically horses), they won't do for you. Take advantage of Harvestcraft's bountiful tree fruit by right-clicking the overhangs. If you're near a village, feel free to rob them of some carrots and beetroots - they might mind a bit, but you'll regain their trust after you vanquish dozens of the undead.
Once you're ready to advance in cookery, you'll need to craft some equipment. The first thing you'll need to craft is the Grindstone & Hand Crank, a combo that lets you grind flour from grain and crack dried clay into bricks. Once you obtain bricks, you'll want to craft yourself a set of cookery - pots, pans, bakeware, and more are in store. While the mixing bowl and mortar & pestle don't need bricks, the rest do - true, copper is a substitute, but save that for bronze-making.
Once you have a full set of cookware, you can start crafting more complicated foodstuffs. Besides meats, fruits, veggies or whatever crops at hand, you'll need a dairy cow and a hen to unlock a good portion HarvestCraft's recipes. Since ROTN uses the Animania mod, several qualifications must be met before you can obtain milk from your cows. As for chickens laying eggs, all you need is a nest (one leaf block, one stick, one wool) for the hens to lay their eggs in.
In the late game, the Rats Mod will come into greater effect for your survival experience. Among other things, this mod allows you to create a Rat Chef, which can turn unsavory morsels into delectable delights! Click here to research more about these rodents.
While there are literally hundreds of recipes in store, many require precise spices and particular ingredients to unlock their potential. However, there are certain recipes that have many substitutes and will likely consist as the bulk of your cooking.
To start, you'll need stock, which can be made from bones, veggies, or meat when stuck with a pot. From there, you can make seed soup, a food which only takes one seed, one stock, and uses the HarvestCraft pot. There is also the vegetable soup, which takes two veggies, stock, and the pot. The third useful soup is the meaty stew, which takes any meat, one flour, stock, and a pot. While this one is more demanding, it sates twice the nuggets of seed soup, and 50% more than veggie soup.
Besides ubiquitous soups, there is the fruit salad, which takes two fruits and a cutting board to create. With fruits in mind, there are the jelly sandwiches, a rather fulfilling meal (if you can make it). It takes a cutting board, one bread, one nut butter, and one jelly to create. Nut butter essentially boils down to either peanut butter, pistachio butter, or cashew butter, which can be made from one cooking oil (which itself is two seeds and a juicer) and the respective nut. The jelly can be made from just about any fruit mixed with sugar in a saucer - therefore, there are over a dozen types of jelly sandwiches!
If you happen to have an apiary on hand, you can grind the honeycombs into honey, a substitute for sugar. Uniquely, it can be used to make honey bread, which only takes one bread and one honey with a cutting board on hand. If you melt the sugar in a saucer alone, you get caramel, which can be used to make caramel apples (one caramel, one stick, one apple).