Two things that I consider important and which are usually overlooked are one, the umbrella, while you need it if you are walking long distance in the rain (heavy rain on your head and body grows tiresome and wears you down over time) the most important reason is for blocking the sun, especially in the desert, and you need a special umbrella, not just any umbrella, the desert is windy and the sand reflective.
A wind handling sun blocking umbrella with a sun reflective top and a dark underside (easy on the eyes when on sand) does wonders for cooling, whether walking or sitting while taking a break.
The second invaluable little thing that takes up no space and weighs nothing, is a mosquito net for the head, a cotton sheet for sleeping is also protection against mosquitos, try sleeping in your car in Houston during the summer and you will know.
G4Free 47/54/62/68 Inch UV Protection Golf Umbrella Auto Open Vented Double Canopy Oversize Extra Large Windproof Sun Rain Umbrellas
https://www.amazon.com/dp/B0BGHCPMGL/?coliid=I371FR09QUVCUF&colid=9XL4DYKH41E6&th=1
The umbrella and mosquito net are great ideas. I currently keep a small umbrella in my truck...will look into a mosquito net. Thanks.