On my commuter, I carry 2 spare tubes, a patch kit, and a topeak road morph pump (as a side note, i also keep a floor pump at work).

I didn't have flat this year until this Monday. Had a flat on my front about 10 min. from the house. No problem. just swapped the tube with one of my spares (I carry 2). About 1/4 mile from the office, another flat on my front. Okay, just walked the rest of the way into the office. Worked on patching the tube. Found 4 holes on the first tube. Not sure if I pinched it while mounting or what, but after all that patching, it held fine. On the ride home, was a block from home and flatted on my rear. Ack. So, I never needed any of this all year, but on that one day, I needed it all.

On my weekend bike, I keep 1 spare tube, stick on patches, and CO2 pump and 1 cartridge. I'm ususally riding with my wife who also carries another tube and another cartridge. Haven't flatted this year although she flatted 2 weekends ago when we were about 3 miles from our finish.