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Wear loose, light colored clothing. Preferably something with ultraviolet protection. You can and will get sunburnt right through a regular shirt.
Brimmed hat is a must, sunglasses would also be a good idea.
I don't know how squirrely the terrain is in Big Bend, but if it's particularly rocky where you're going, and your ankles aren't the sturdiest, you may want to opt for footwear with solid ankle support.
Be absolutely certain that the water sources along your route are reliable. If they aren't, or you can't confirm, plan accordingly. For my money, even when local water sources are available, I never go into the desert in summer with less than a gallon on my person, bare minimum. But then the south central Mojave is usually pretty dry, so maybe things will be easier for you.
Bring plenty of high energy snacks, preferably a bit salty. Think jerky and trail mix. Munch on those constantly while you're on the trail, and don't eat a full meal unless you're well hydrated.
Familiarize yourself with the signs and symptoms of dehydration and heat illness. I know you say that triple digit temps aren't expected, but better safe than sorry.
Map and a compass, goes without saying. GPS if you've got one.
Pretty much, backpacking in the desert is like backpacking anywhere else, save for the heat, the lack of shade cover, and the greater difficulty navigating and sourcing water and firewood.
