Foodstuffs such as bones, meat, etc., not good because it attracts rats and vermin generally. Leaves should be composted separately from other material, as should whole fruits and even fruit peels like orange or grapefruit, though if its only occasional, the addition of fruit peel isn't too bad. Grass cuttings are fine, but not dumped in a large pile, should be spread in thin layers throughout. Woody materials like twigs or branches which have not been shredded will take forever to rot down, so not great additions. If you are using a hot composting, aerobic method, then you can add weeds, if not, don't put flowered weeds on the heap.