Neither of these are particularly novel strategies, but I do a combination of:
- sheet protectors in a 3-ring binder (US legal-size to accommodate US+UK and archival mounting corners for small pieces).
- acrylic sign-holder stands placed at the back of a shelf (creating a nice background for 3D objects).
On the slightly more novel end, I've considered looking into those wall-mounted flip-style poster display racks you see in stores. That could make them easily accessible while using a fraction of the wall space.
I collect banknotes and I would recommend lighthouse products for storage. They have banknote sheets you can get that fit many contemporary bills. The also have good semi ridid banknote holders that seem to hold the bill nice and flat so as to avoid damage without going for a full acrylic case.