Yes, refridgerating them helps them last longer because the cold temps make them go into hibernation. I've heard of people using anything from oatmeal to the bedding that you can buy specifically for them.
I dont refrigerate mine anymore. They dont really eat when they are hibernating so they arent eating all of the nutritional stuff that is mixed in with them. The stuff the petstore puts them in is not very nutritious I recommend using dry oatmeal (ground up in a food proccesor) mixed with fish food flakes for protein, calcium powder and gutload sold at the pet store. I also mix fresh veggies in for them to get moisture. (Grapes and carrots work well).