Food is one of the critical needs for a Slugcat's survival. Each Slugcat requires a certain amount of food to hibernate, while excess food eaten is stored in their stomach for the next cycle.
Some food is found in the form of immobile objects such as fruits, vegetables, and fungi, while others are living creatures which the Slugcat may need to kill before devouring. Eating only one of the two varieties for several cycles straight is the key to two of the game's achievements.
Due to how food respawn mechanics work, it is beneficial for Slugcat to attempt to harvest and store food that is consumed on a future cycle in the current one: this starts the food's respawn timer in advance by possibly up to several cycles. This can make a critical difference if circumstances force Slugcat to linger in a region temporarily. This does not normally apply to Popcorn Plants, Batflies, or large Centipede variants, though, as they cannot normally be stored for future use either due to being immovable, perishable, or too heavy to transport respectively.
The following are creatures that are edible for the three Slugcats of the base game and almost every Slugcat in Downpour. The corpses of all creatures are edible for Gourmand, Artificer, or Hunter. None of these are edible when playing as Saint.
SPOILER WARNING This section contains major plot details. If you have not made significant progress in the game, then it is recommended that you read no further!
The Spearmaster is one of the new playable Slugcats in the Downpour DLC, and has a special relationship with food that is completely unique amongst all the other Slugcats. Having no mouth, the Spearmaster instead siphons nutrients from living enemies using self-made spears, usually filling up to 1 hunger pip per hit, though there are some exceptions like Eggbugs, Giant Jellyfish, or the extremities of larger creatures like Vultures. This allows the Spearmaster to 'eat' traditionally inedible creatures like Leviathans or Pole Plants, while also making it impossible for them to eat some staples of the Slugcat diet like Blue Fruit or Slime Molds. They are also still able to make use of consumables like Mushrooms or Karma Flowers with this unique consumption method.