lots of really good suggestions here.
Bottom line is being very aware of taking in lots of luiquids, keeping on top of it. The times I've had to ride in 90s a lot, I've generally been lucky in that there have been towns and stores available to be able to go in, take advantage of air conditioning and buying some cold drinks, I find getting some cold drinks in really helps.
Taking shade breaks and even a nap in the hottest parts of the day has worked for me also.

I think to when I was younger, I figure Im smarter now and listen to my body more, and am much more careful of sunscreening well, drinking lots regularly and taking breaks more.

Doug--that's a cool idea (sic), I really like that. I've used cut up pieces of those blue mats to make protective stuff for laptops and camera stuff in the past, but it completely makes sense to use it for insulation, great idea.
Will store that one in the 'ol noggin for future use.