I keep the 120 spools and 35mm canisters in a waste-bag where I develop the film, not sure what to do with them though, always good to have a spare spool when you get a new 120 camera, and a spare 35mm canister for bulk-loading, other than that.....dunno.

I toss just about everything else (backing paper and the end of the 35mm film that I cut off).