For guts, I’d include heart, liver, and generic entrails/intestines. For small animals you could include a generic giblets, which would realistically be a combination of these - just too small to use for certain recipes. Alternatively, it just translates to smaller yield. A big animal will yield a heart AND a liver, while a small one will only give giblets. You’d still be a meal behind on that count.
Heart could stand in for a number of meat items in any of the already-existing soups/dishes, or be eaten cooked as-is.
Liver: Eaten plain, super gross (eww liver). Eaten plain and cooked, is good nutrition but meh for morale. With onions, wild herbs and or jam (deluxe recipe), becomes hearty AND delicious. (Yes jam. Trust me, a little sweetness with the savoury of properly cooked liver is amazing.) The health boost is worth considering as a tradeoff for the lack of morale I’ve suggested.
intestines: useful when cleaned thoroughly for making own sausages/hotdog-type-things. I can’t remember if either of those can be smoked to make them last longer but a nonperishable food result would be nice to add to the list.
Giblets: Not as sure what to do with these. Could stand in for meat items in other recipes, like for soup stock/soups, add the deluxeness to omelette, etc. Could be cooked and eaten plain for a little nutrition, as it’s basically tiny meat. Maybe they could be added in to those sausages we’re making up above to make the meat stretch further.
I am kind of against adding too many differentiated bones, unless it’s large, small, and tainted. Size-wise that would render crafting with them akin to making needles from heavy sticks instead of splintered woods. Considering the bone armour we already have in game, I made the assumption the skulls were always getting used for the helmets, personally. Even if not mentioned explicitly.
If I HAD to pick another bone item, I’d go with teeth. Mostly for flavour, take them from my enemies killed, have a tooth added to inventory every time I do too much meth and get that message about having too many teeth. Might get weird if I manage to do that to myself more than 32 times, but I don’t usually live that long.