I lost my earplug case recently, so naturally I made one. It doesn't really have a clasp (I still can't figure out how to model clasps), but the friction of the joint seems to be enough to hold it shut. There's two versions because I own a couple different sizes of earplugs. The 'short' case will fit most standard light earplugs, whereas the 'tall' case is required for heavy-duty or weirdly-shaped ones.

And of course I put little ear designs on the sides, just in case I ever forget what the tiny box on my nightstand is for.