Bread, meat, canned soup, bananas, corpses... anything that looks edible.
You will eventually get hungry and ultimately you will die from starvation, so if you want to live a little longer you can e)at food to gain nutrition and sustain hunger. Rotten food is usually bad for your health, though.
Praying to Seges will fill your stomach if you are in a good relation with her, or empty it if you are not.
Several kinds of food stuffs and monster corpses have unique additional effects.
- School food - School food will poison you, but it may also raise your Endurance
- Carrot - Eating carrots will raise your Perception
- Holy Banana of Oily Orpiv - Eating the holy banana will cause you to be Overfed for a very long time. The downside to this is that since you've gained a lot of weight, your Agility will inevitably go down. It will also raise all of your stats (AStr, LStr, Dex, etc.) by 1.
- Human corpses - It is possible to eat a human corpse, but doing so is an evil deed, and will make your alignment slightly more chaotic.
- Rotten corpses - If you see a food item with flies buzzing around it, it's best to stay away. If you do eat a rotten food item, or an orc corpse, then you may get a parasite inside your stomach, which continually eats away at your stomach and can only be ridden of by vomiting.
- Mutant corpses - such as carnivorous bunnies and mutant asses will cause you to polymorph randomly. If you have PolyControl this is okay, but if not then it's best to leave these corpses as a last resort and to only eat them if you are hungry.
- Chameleons - have the same polymorph effect.
- Zombies - eating a zombie corpse will give you leprosy.
- Poisoned corpses - eating spiders, skunks, or snakes will poison you, which will make you vomit, and you'll end up even hungrier than before. So this is never a good idea.
- Acidous corpses - Since dark frog blood is acid, eating one of their corpses will cause acid to flow through your blood stream. This will most likely kill you.
- Werewolves - Eating a werewolf corpse will give you lycanthropy, which will cause you to polymorph into a werewolf randomly
- Floating eye - Eating a floating eye will temporarily give you ESP, which enables you to detect intelligent creatures even if they are not humanly visible.
- Blink Dog - Eating a blink dog corpse will give you TeleControl.
- Magical mushroom - Eating a magic mushroom corpse may have a wide range of effects, from Polymorphing, to TeleControl, to Levitation, to Hasting or Slowing.
- Unicorns - White vs. Gray vs. Black