I work outside yearround. Cold weather is harder for me to tolerate than hot. When it is above 90, I wear light color polyester/cotton blend clothes. 100% cotton just gets too heavy when soaked with sweat. But the blend promotes evaporative cooling. I take frequent short breaks in the shade and drink plenty of fluids. Powerade works for me much better than plain water, certainly better than sodas. I always wear a hat, also light colored on hot days. I don't use airconditioning in the truck going from one jobsite to another. I have recorded temps of 117 degrees recently when setting a new dark blue pool liner. It can get even hotter when working in a new excavation with shiney steel walls all around. In these conditions work smart. If you see signs of overheating in yourself or others, stop and cool off. Even if it means working for fifteen minutes and resting for ten. Moving air helps, even if it is hot air. I have 48" heatbuster fans I can set up to blow into excavations.
Keep in mind that a tool left laying in the sun can easily get too hot to pick up. As a contractor responsible for my workers, I have to keep an eye on their condition. Some are young and inexperienced with heat, and it isn't uncommon for them to overheat. I have to make them take breaks. I don't eat a midday meal. It seems to take too much of my energy to digest a meal when I am hot. I eat a very light breakfast, if at all. I go to work earlier and, if the work requires a long day, take a long midday break and come back after the hottest part of the day has passed. Here in Southwest Tennessee that is usually 1:00 to 4:00 P.M. I have been known to show up before daylight, send everyone home at noon and come back in the early evening to work under lights.