Here is a link to the "Grabber" brand of chemical hand warmers. They have a great selection and was recently inducted into the "Field and Stream" Hall of Fame for a great product. From what I have read, these are the best on the market. I am going to order a pair for my shoes. They make warmer shoe insoles, toe warmers, hand warmers, body warmers ect...
http://www.warmers.com/
Dennis