I have a trunk bag in which I carry a spare tube, a patch kit, a multitool, a pump and a set of irons, along with arm and leg warmers, a light rain jacket, and a lock. I commute 30 miles RT daily, and have had very few mechanical issues (last flat was over 4000 miles ago), I do most of my own maintenance and am pretty good at keeping up on things. On this mornings commute, while starting off from a red light, my chain broke - the chain is a SRAM 9 speed chain, with 1500 miles on it, and it had stretched about 0.75% - It was going to be replaced this weekend even before it broke. At the time the chain broke, I was with another commuter, and was chatting with him and he stopped to help. Neither of us had a chain tool or a pair of pliers with which to repair the chain. I ended up flagging down a Cable TV service van, and borrowed a pair of pliers from him which allowed me to get the chain fixed enough to get me the last 2 miles to work.
In any event, it got me thinking - what tools do other regular commuters carry with them on their commute. How many of you would have been self sufficient and been able to get back on the road with a broken chain?