I haven't spent much time in the desert so what I have isn't really survival so much as it's comfort: - Bring something or improvise something to move air. Yes, you should have water, and it will evaporate quickly in the dry air, but in a car or under some shade, the lack of air movement can make one miserable. Personal misters go a long way to keeping your spirits up too. I was trapped in a compact car with 3 others in backed up traffic in Nevada once, and even with the windows down (we dared not overheat by running AC) it was intolerable. I broke out some notebooks and other items and we used them to fan ourselves. It made that sweat shop a little more comfortable.

One other problem I've read (never experienced) is that a lot of desert shelter is already in use by other criters staying out of the sun... so exercise extreme caution in moving into any natural cover. Some snakes are virtually invisible, but at least a rattler will let you know it's there if you walk slowly enough to not startle it into striking (again - what I've read, not done). Most NA snakes don't want to bite you. Now, go to Africa or Oz and that may not be the case... they got some aggressive buggers.