I have three toolkits depending upon the situation. Just riding around the neighborhood or a quick ride across the bridge (sans mess bag) I carry a 16 gram c02, microflate c02 nozzle, two tire levers, patch kit, and 15mm wrench. it fits in my pocket and the idea is that if something big happens, i'll just jump on the subway. 2nd kit is a bit bigger but fits in a small jandd saddle baq which i usually throw in my bag unless i'm bagless. It has 16 gram c02, second wind mini pump/c02 pump (nice to have a backup hand pump if i run out of c02), tube, tire levers, front and rear knog frog lights, serfas multi tool, and a 15 mm wrench. my last one is just the second one but with a second tube, a couple more c02 cartridges, and a larger topeak mini pump, plus a rediculously large map of all 5 burroughs. that one's for long rides with fix it or carry it home implcations.