You can also boot some cuts/gashes with folded paper money. Just remember to carry a $1 bill. One time I needed to boot a tire and only had a $20. It was all the cash I had with me. The nice thing was that I forgot about it for a couple of weeks until I put on a new tire. It was like finding money in the pocket of a pair of pants I hadn't worn in a while.

I have head of some people using PowerBar wrappers for boots.