Use a cellular telephone or a CB radio to call for help. If none of your friends or family are available, call 911.
Set up a tent for shade and collect wood and brush for a signal fire if you can't reach anyone. Don't panic and inventory your resources, especially if it looks like you're going to be stuck for awhile.
Stay with your car, which can provide shade, shelter and a beacon for aircraft and rescue parties. Remember your horn can be heard from far away and your headlights will make you highly visible at night.
Carry a spray bottle and spray it in your mouth to conserve water. Spray your skin to prevent dehydration if you have plenty of extra water.
Stay calm, relax and conserve your strength in order to make your food and water supply last longer. Always watch for aircraft and other searchers.