It's surprising how important those cardboard sleeves on your coffee can be, but if you'd like something a bit more durable, you can make your own reusable cozy out of an old belt.
Whether your coffee is so hot that a thin piece of cardboard doesn't help or your coffee place of choice seems to enjoy burning your hand, this is a quick project that will save you coffee drinking pain forever. All you need is an old leather or fabric belt, some thread, string and a sewing needle (though if you don't have any sewing skills, don't worry—it's pretty simple). You'll also need one of the cardboard models to act as a template. Then it's just a matter of cutting up the old belt, sewing it together, and throwing it on your cup as you run out the door. Hit the link for the full instructions.
Recycled Reusable Coffee Cozy [Instructables]