One item that you can't do without is a pair of tire levers. If you've never used them before, you probably haven't had a flat tire!
If you do have a flat tire on one of your rides, you'll be happy you included a pair of tire levers in your tool kit. These levers are made by Pedro's and have an excellent reputation as far as utility, ease of use, and -- most importantly -- durability. The secret is a proprietary plastic blend composition and a unique chisel tip shape. Dual spoke hooks will also help you remove any tire.