Food leftovers: vegetable scraps, coffee grounds and egg shells won't smell, you cansafely compost those alongside the leaves, and it'll greatly improve the quality of your compost. Just avoid animal leftovers besides eggshells.
Yep, this. I rinse the egg shells first though.
Otherwise, veggie & fruit scraps and coffee grounds go straight into the dirt, about three inches at least. I bury them in a hole, pile on three to four inches of dirt covering, and put a flat, large rock over it. No problem with animals digging up anything yet. The worms in my backyard take care of everything within two to three weeks, as long as I make sure the area is sufficiently watered.
(We have a relatively large yard and so far, no smell.)
If it's just leaves (like salad leaves), I'll bury it without doing anything else. Otherwise, if it's lots of scraps, I'll mix in dirt before I bury all of it.