I second (third?) the spoke idea. On long rides, I carry an extra spoke. But I don't bother if I'm riding where I can get help. I've only broken a spoke once, and that was in town. I just used the bus fare I always carry to get to work and home again (thank you COTA for the bus bike racks!). At a minimum, you should make sure you have a spoke wrench. Most good multi-tools have one. In a pinch, you can tighten spokes on either side of a broken one.