Found this at the thrift store. What is it?

[P]

Hehe it has many uses.

[DoctorDirty]

[L___E___T]

I can't believe I forgot all this time mine were lunchboxes before I decided they were cartridge holders!

Will you be hanging on to it?  If you decide to sell let me know, I wouldn't mind adding another to the set.

[DoctorDirty]

I think I'm going to keep it and use it as my new bento box.