I keep sets of keys in the net bags that I buy grapefruit in at the store, after washing, of course. That way they are sure to dry properly, since I always wash them well before storage. The net bags go into a cardboard box.
Keyboards for deep storage get a layer of large bubble wrap over the keys, and a sheet of cardboard over that. Then I wrap in a plastic sheet and tape it shut.
I have tons of old business cards that I put in each lot with details on what is inside.
I use US Post Office "game board" priority mail boxes if I don't have the proper box.