Is a lock a school supply?
It can be. Some schools lockers require your own lock, or it can be used for locking a bike, a box or just about anything with a chain or hole. This is a nice closer look at the Sonic from the early 90s series of character locks. (See that on Misc. Japan) Sonic is metal, with the lock arch coming out of his head. The key fits under his feet. It's a cute little figure with blunter details (since it's metal) the paint is likely enamel. As you can see here, it comes in a little transparent plastic 'box', with single card of instructions in the back.

Due to the small size & simple packaging, it's speculated this could be from a prize machine, but nobody's ever proven it. The other characters would work similarly, and be in a similar package type.