Bones from roasted meats always go into the freezer for stock; if I bone something before I cook it, it goes into the freezer as well. Uncooked shrimp-shells go into the freezer for seafood stock. If we have leftover steamed crabs, we remove the lungs and freeze the rest for crab soup. I don't usually have enough veggie trimmings to amount to anything. If I think about it, I'll put poultry fat into the freezer (shmaltz!!), and if I do several roasts at a time, most of the drippings will go into the freezer as well. Parmesan rinds go follow the parade into the freezer to boost up soup or chicken stock that I know I'll use for risotto. | 
Normally discarded material? 
