My husband was gifted with this thing that goes around your neck. It is about 8 inches long, tubular and has these beads in it that absorb water. You leave it in water (cold) for a few hours or overnight and it expands as the tiny beads absorb water. Keep that thing around the back of your neck and it will help to cool you down all day. It takes a long time to dry out. I don't know what it is called though or where you can get one, but I think that they would make great playa gifts out there! Maybe sporting good stores carry them...

A personal mister is nice to have around to spray yourself and others down.

I have to wear loose cotton clothing during the day. I will dress up for evening, but for daytime, it has to breath or I won't , hahaha!

If you're sleeping in a cargo van - is there any way you can rig up a shade structure over it? The key is to have at least 8 inches between the top of your vehicle and the shade cloth. Just draping cloth or something directly on it won't be very effective, but some shade with a little air space will make all the difference.

Arizona Gigi's guide too staying cool and maintaining your vampirish pallor :-)

All though this year we are bringing a pop-up trailer in the past we have always tented it.

first we have a carport or shade structure
under it goes the big tent, under the rain fly of the bid tent goes one big tarp
In the big tent goes the little tent, little tent also has a tarp under the rain fly and a thick blanket draped over the whole tent
in the little tents is our bed/ air mattress
In the opening of the tent is our evaporative cooler, the rear end sticking out for air intake. The best of this is the moister makes the air both cooler and less dry and makes all dust fall so its a dust free space. We allow no clothes or shoes in the little tent. this pulls low amps and lets a small generator run it all day long.
this allows you to sleep through the hat part of the day which as any real desert dweller will tell you is siesta and the best idea in the desert.

If you must travel out do not make the mistake of thinking less will keep you cooler, it won't wear cotton layers that will cover your head arms and neck dip these in cooler water and don't for get a good loose weave hat for shade, a parasol, SPF 30 of high sun screen and WATER. Beer may sound refreshing and by all means have one but drink a glass of water first then have your beer.
Remember the quickest way to cool your self is ice or cold on the back of the neck, this is where blood runs closest to the surface and will cool you off quickly.
do wipe your face and hand and feet and let your feet breath if you can they shed a lot of body heat.

and if it gets really warm and you don't have my fancy contraption lay in the shade with one wet sheet under you and one wet sheet over you (face and all). the evaporation will make you amazingly cool and let you rest peacefully.