That and an extra set of points, for those of use w/ stock distributors or Pertronix.
I can do one better. I once had to get towed because my carb started flooding gas into the engine. Only after getting towed home did I figure out the carb float got stuck. As it turns out I didn't even need to have extra parts on hand. I just needed to knock the side of the carb w/ a wrench or hammer to free up the float. Lesson learned in my younger days (and knowledge used later on the trail)