Im kinda skinny myself cause I have a high metabolism. Meaning I burn fat really fast. And I've been doing a bit off research, best food for muscles are meats, and eggs.
For fat is
- Butter
- Ice cream (contains milkfat)
- Cheese
- Meat fat
- Coconut oil
But for some odd reasons peanuts and any other type of nuts are good for both muscles and regular fat. So if I were you, I'd stick with nuts.