I am not overly concerned with weight so in addition to tubes, Pedro's tire levers, Park tire boots and a Topeak Road or Mountain Morph (you never run out of air), I carry CO2 cartridges and inflator. When it's 90°, a three second fill is so much better than pumping a tire for five minutes (I never flat near shade). I also keep a 1"x1" piece of cloth or a cotton ball stuffed in my bag to rub on the inside of the tire to find what ever might have caused the flat. I started the cloth or ball after I discovered an industrial staple by bloody hand. I also bring a patch kit to lend to other unprepared riders. A presta/schrader adapter ($1.00) is handy if you flat near a gas station.