Alternator,Starter, I always think of the little stuff that goes out when you don't expect it and then you have to go to a parts store and get a new one if nothing else you can always use them for core charges so you don't have to have yours off before you can get a new one. Light bulbs is also good to keep in stock and don't take much space to keep. Even cut some of the plugs like tail light sockets never kow when you need one.