Driving in the dessert in August means a bunch of common sense things, I think

- The extra water makes a lot of sense. You can get dehydrated very easily, without even being out in the hot air while driving. That is, folks don't want to stop so they decide not to drink water -- that's not good in the long run for them. So take some extra water and make sure you drink water on the drive. The extra is for emergencies, but you should be driving the whole time anyway (the air is very dry...)

- Take a cell phone that works. There are emergency call boxes every couple of km along the way, but there is also cell phone coverage 99+% of the distance. Call 911 (emergency) if you need to.

I should note the freeway is typically moderately busy, and a major interstate route. It's patrolled, both by air and vehicle -- but its such a long distance that if you just wait for a highway patrol vehicle, it can be a fairly long (hours) wait before they see you. Cell phone is best.

- Dress appropriately. It's going to be hot. And the ground is going to be hot. If you end up walking on the desert surface, its not sandy and can be 20C hotter than the air. A pair of good walking shoes and appropriate clothes to be comfortable in makes a lot of sense, regardless.

- Sun protection. Sunglasses at a minimum. If you're of European heritage (and particularly northern European heritage) you can be sunburned in like 20 minutes in the sun. Having sunscreen (at least level 30), a hat, and sunglasses just makes sense, regardless. And use them -- sunscreen in the morning, re-apply mid day, and wear the sunglasses, even when driving.