I ride in some very remote areas. It is possible not to see a car for an hour. Recently, I broke a chain. Luckily, I was close to a bike shop, so I could get it repaired. It started me thinking "what else should I carry"? I purchased a chain break tool and a couple of quick links. Now, if I have chain problems in a remote area, I have that base covered. I also carry two tubes, 3 CO2's, tire levers, 3/5 allen wrenches, a patch kit and a emergency pump. Cell phone and $$ are standard too, although there is no continuous cell connection where I ride.