Having a car charger is a great idea, not even for disasters but for minor emergencies. It's easy to let your phone run down, and kinda silly to find yourself with a car with plenty of electricity, a flat tire or other vehicle problem, and a cell phone you can't use because the battery is dead.
For major emergencies, a cell phone might work. A ham radio will work. To me, depending on a cell phone for communications is exactly like depending on any other utility - gas, electric, etc. Eventually service will come back, but it may be a while.