AS much water as you can comfortably carry, proper clothing & boots, sun hat's(2), sun glasses (2 pairs) signal mirror, compass and a decent map for each member of the trip. Insist on a proper safety briefing on the does and don't of a desert enviroment. Institute a buddy, buddy no lone zone policy.
To me, somewhere like Death Valley can never be described as a "normal" camping trip. Simply because the enviroment is so extreme.