You never know exactly when a disaster or emergency may strike, especially out here in earthquake country where I am. So, it is important that you have enough supplies in case your car breaks down, you have to wait for someone else to come along or if you have to walk to safety.
In addition to the more common items like jumper cables, or emergency car starter, and work gloves be sure that you carry some of the following items.
You'll especially want the food if you need to walk to safety or to your home. In the case of an earthquake with major infrastructure damage you'll most likely have to walk for several miles to reach home.
If you are stranded in the middle of no where it is best to stay with the car and wait for help. If you need to leave the car for safety reasons, stay on the road at all times, you will be more likely to get help and be spotted by someone.