On my road bike all that I carry is the stuff that I need to fix a flat tire. That's all the tools that I carry for my car too. On my mountain bike I also carry a few allen wrenches and a chain breaker. Whenever I ride I make a mental list of unusual noises and anything on my bike that isn't working to my expectations. I immediately take care of that stuff at home so I don't have to do much in the way of maintenance or repairs while on the road.

I'm always surprised when I read how much stuff some guys carry with them on every ride. They always say their bike doesn't need it but they're always helping out other people. I guess that if I was always finding prople who needed on-the-spot bike repairs I might start carrying some additional stuff too, but I'm not seeing people who need help in my weekly travels.