i prefer a hand pump over CO2. if you mess up, you are left with a flat. and i get so many flats i'd have to buy alot of co2.

pump
lever
patch kit
tube
15mm wrench to remove wheel (if not quick release)
pocket knife/multi tool

I always try to patch first without removing the wheel. if I can't find the puncture or if it is torn badly i will replace the tube.