Introduction
In the case of an emergency, you should have at least one survival kit on hand, and perhaps more such as in your car, office, etc.
Your first priority should be to take care of any medical emergencies. Then:
Drinking water filters, purifiers, and more
You'll also need to provide for clothing, food, shelter, medicines and first aid, and various other items that will be covered in the near future.
Also, Trinity County's suggestions are here, MeFi has suggestions here, and a SF Gate reporter has more here.