I've used black electrical tape on my GumPintoids, but you can also use a piece of flexible magnet strip, or a small ceramic magnet (easier to remove for exposure if you glue on a handle of some sort), or any sort of tape with a black piece of cardboard (matt board, poster board, etc.) to cover the actual pinhole. I've also used camera shutters, though so far only in converted cameras that already had a shutter...
You should be able to put 120 film in a Pintoid -- lemme check...
Okay, I have half a dozen Everest gum tins awaiting conversion; they'll accept 120 film of about 6x6 dimension; it's a snug fit for width and you'd have to trim corners to fit in a longer piece. I don't have a standard Altoids tin handy, but I've heard 2x3 sheet film just nicely wedges by the corners in those, which means they should also accept 120 if you get the length just right. I'd suggest cutting to 6x6 and using small rails to hold the film against the inside bottom of the tin; that way you don't have a major problem if your stop slips in the dark and you cut a roll a mm or two too long or short.
BTW, the mini-Altoids tins accept 35 mm film, and are the basis of Marcy Merrill's "SpyPintoids" -- very tiny cameras using approximately square chips of 35 mm. I've got a couple Starbuck's mints tins here that also will hold similar film, but those are no longer available from Starbuck's.
BTW, if you're shopping around for tins and like cocoa, Starbuck's currently has a 3-flavor pack of cocoa that includes *three* pinhole cameras -- 120 degree sectors of a cylinder, so the three tins pack like a single can. The tins look as if they'd hold 4x5 on the curved side with the pinhole in the center edge to make nice curved film semi-pano cameras. I'm still debating -- I'd never drink the cocoa, but my wife probably would; however, I'm about 15 tins behind on pinhole camera making and can't really spare $15. Maybe the tins will turn up at Goodwill...
