Great Posts....living in Az for 25+ I would offer...
Plan ahead..how you hydrate the day(s) before is every bit as important as the day of.
Keep the sun off the back of your neck and while long sleeves for some seem to present a mental paradox with regard to heat, they are not. (A moist neckercheif works great for the neck) or turning the collar up on a polo. Many times, even safari style hats don't protect your neck 100%. Have for years watched workers harvesting melons, lettuce, etc in 110+, recently irragated fields and you won't find one wearing short sleeves.
Hats...obsolutely.. ...
Don't be fooled into thinking that sun "screen" = protection from sun "heat". It does not.
LP...I play a lot of golf....and while long sleeve (at least to forearm), loose fitting, lightly woven, light colored cotton may not be the fashion de jour in the summer I have been known to golf in such if on a course with little or no shade to be had during waits.
Having face, ears and forehead carved/grafted in the last few years and situations where back cramps, for me, one sign of overheating....abov e represents what I have learned and should of done better, earlier in life.
my .02....be well, be safe