These are orthodontic rubber bands, the little ones that hook an upper set of braces with a lower set of braces to coax a jaw into some unaccostomed position. They are also the reason band members with braces get an unaccustomed amount of attention.
Someone walks into rehersal with a new and uncomfortable looking hardware collection wired across his teeth. The reaction is sympathetic:
"How are you getting along with them? Don't really miss the popcorn?"
"How's piping with 'em?"
"Sixteen months, eh? Oh, it'll go by before you know it."
It is only after a properly sympathetic pause that it is appropriate to add, in the most offhand way possible, "Oh, by the way. . .emm, I don't suppose the dentist gave you any of those little rubber bands, did he? Oh no. Just one would be plenty."
I live quite near an orthodontist's office, so it was only a matter of months before it would occur to me that perhaps rubber bands could be procured right at their source. Oddly enough, they can. Indeed, the receptionist kindly gave me a whole bag of them, for free, with no orthodontic obligations attached. . .Who'd have thunk it?