Extreme temperatures are always possible in DV and winds are likely (wait til you get to Ubehebe Crater). Rain: not likely at all (but I've been rained on out there).
Some suggested items to bring include: water (lots of water), tow strap and full-zie shovel, tire repair (plug) kit, jumper cables (one set per group), flashlights/batteries, sunscreen, hat, jacket, blankets, work gloves, shade (tarp), FRS/ham/cb radio (sat phone), first aid kit, food, more water than you think you'll need, and your off road survival kit.
How many vehicles are going?