Alternative idea: a ring of keys(if that can count as a singular object). 

When in weapon mode in limbo, the keys separate and fly around at the wielder's will. 

EDIT: The Model T Ford was first produced in 1908, can that be a Tsukumogami?

Does a larger item have more power? For instance, something too big to be reasonably carried in secret?

What about humans remains? Or animal remains? Do those count as objects? Could I use a whole-ass mummy?