Hah! I use strips of old innertubes for that. I almost always carry 3 or 4 of them with me. Also use them to tie my pant legs and keep them out of the chain. Don't cost me a dime!
also useful for attaching small objects to my rack, etc (Or bigger objects... tied a couple of tires to the side of my rack with them the other day to bring home for my wife's bike.