I'd make sure to add a shovel, tow rope, bailing-wire, pliers, jumper cables, a tarp, ropes, face mask/bandana, goggles (that allow glasses, if you need them, like I do). If there's a bad dust storm, you can tie the rope/twine to the steering wheel and to your belt before venturing outside. People have gotten lost when they slipped and fell while trying to navigate from the front of the car to the back door during a dust storm or blizzard.

If your local emergency services has reverse-911, you should register your cell phone with them so they can notify you if there's an emergency.

You may want to look into amateur radio. That isn't dependent on the interconnected cell towers. A cell phone is great as long as the system and power is up, and it isn't overloaded, as has been seen when there's an emergency.
With a mobile, or hand-held, amateur radio, you can listen to, and converse (if you're licensed) with other operators to stay updated, or request help if other methods of communications are down. Some who prepare for emergencies include amateur radio as one of their steps. If there are some in the area, that can help as well.
Some repeater clubs publish coverage maps that can help to see where you can hit a repeater. http://www.levinecentral.com/repeaters/google_mapping.php?State=CA or http://www.scirainc.org/repeaters.php

Depending on the type (class) of license you get, and equipment used, you can communicate within your county, state, portion of the country, or even across the country. You can get your license and a fairly inexpensive hand-held radio for under $100. A mobile radio with an entry-level magnetic mount antenna can be had for under $250. With an entry-level handheld radio I've hit a repeater almost 20 miles away, adding a magnetic mount antenna, I've talked to someone 75 miles away (simplex, direct radio to radio), and when a higher powered mobile radio with the same antenna, I've hit a repeater over 100 miles away.
With the basic hand-held radio, I hit a repeater about 15 miles away, and the repeater was linked with other repeaters across my state. I talked to my brother who was connected to a repeater 200 miles away.
Even an old CB radio may be useful.