Portable solar umbrella
Having recently spent a bunch of time in some of the world's hottest deserts, I wonder why no one has marketed a portable solar umbrella hooked up to a drinks cooler, or small cooling fan, or one of them electric cooling collar contraptions. Googling for 'solar umbrella' points to large unwieldy umbrellas good for patios and backyards - hardly convenient for hauling around.
Making these should be a no-brainer. You'd have to fix flexible solar panels on top of a folding umbrella, and run a wire through the handle. I bet somebody with a low cost production facility already making umbrellas could easily adopt this and do a pilot batch. You'd start by marketing in the Sky Magazine and the like, hopefully, it catches on to start mass production.
Reward: I'd personally test one of these in the Atacama Desert in Chile next July (a week long 250km ultra run).