Fat

Fat is the last (not least) edible part from a slaughtered animal. Fat is actually one of the most filling foods by weight, but the fact that you get so little of it means that it doesn't make a particularly useful food source.

It can be used as food and for tanning skins.

You normally get a little more fat than needed to tan the skin of the animal you got it from, which means you can eat the rest as a replacement for the time spent tanning.