Always inform someone of your plans:
Tell a spouse, friend, neighbor - of where you are going and your expected time of return. Provide them with a map and the route that you expect to take and STICK TO YOUR PLAN. Make sure your backup person has the appropriate emergency phone numbers and description & license plate of your vehicle.
You should have at least 1 gallon per person per day, plus an extra 5 gallons in the vehicle. Drink water if you have it. Do not ration it if you have enough.
If you are going on a long hike and if you know that you are returning by the same route, you may want to stash some water along the way for the return trip. This will help eliminate some weight. Do not forget to "mark or waypoint" the place where you dropped off the water.
Depending on the length of the hike, Take from TWO to FOUR 24-ounce bottles of water with me. One can be frozen solid and the other three filled half way up, frozen then filled up the rest of the way with cold water. This keeps the water a little cooler a while longer.
If water is in short supply, try breathing through your nose and not your mouth, which will help reduce moisture loss.
When you urinate, note the color. If your urine is dark, it may indicate that you are not getting enough water. If you have the water, drink it.
No beer, coffee, or booze as these will dehydrate you and make your situation worse.
We recommend 2 Garmin 60CS series or Rino series GPS's. - We chose this model because the antenna on these models gets better reception in narrow canyons. The second GPS is used for backup. If you cannot keep 2 GPS's with you, ensure that you have another backup method of navigation. See Compass below.
Use mapping software - Delorme topos, National Geographic topos, and All Topo Maps are good sources. Upload waypoints to the GPS to mark the roads and to mark your route in and out of the washes/canyons that you expect to hike.
ALWAYS, always, always mark a waypoint where you parked your vehicle even if you are on a paved road. How many times have you left the vehicle and lost sight of it in the matter of minutes because of the washes, hills, and just low knolls. Sometimes the old, "I think I parked it just over the next hill" doesn't quite cut it, unless you are parked at the mouth of a canyon and there is only one way in and out. If you have for some reason neglected to mark where you parked, some GPS's can "project" a waypoint in case you do not want to "back track". Many times I want to take a different route back to the vehicle and marking a waypoint where I parked allows me to do this without too many problems. If you do not have mapping software, use web sites like: Google Earth: http://earth.google.com/
If you have a compass, KNOW how to use it. Many people carry one and don't have a clue how to use it. Consider taking an orienting course through the local community college or Outdoor Equipment places such as REI.
Should be lightweight, light colored, long pants and long sleeved. Have a hat available. Have something to cover the back of your neck. A sunburned neck is a killer. Some hats provide a flap for protection or another piece of clothing can be used. Good comfortable boots with non-slip soles if possible. No tennis or street shoes.