Some tips I learned growing up on a farm where I was forced into slave labor;
Wear long white sleeve shirt and pants. The baggier the better. Same concept at desert nomad clothing. Except I live in humid environment so I actually want the wind to wick away sweat when possible. You'll feel much cooler like this than you will in short sleeves. Long sleeves and pants keep the biting flies off of you as well.
Sounds counter intuitive but heavy ankle length boots are best. Keeps feet dry and the steel toe will cool down much faster when you do manage to get out of direct sunlight or into an AC cooled room. Wear breathable diabetic white socks for the same reason you wear baggy clothing. You want your feet cool and dry so they don't form blisters.
Smoking or being new a fire of green wood will keep away biting insects. You don't have to inhale. Puff on a cigar to keep it lit and smoldering. This is one of the main reasons why people smoked in the old days along with the fact that it allowed them to carry an ember that wouldn't be forgotten. If you aren't okay with smoking I find a fire horn/bundle works almost as well. Smoking works better because biting insects are most annoying on your face. Which is well protected by something like a cigar.
Try to work near large bodies of water preferably running water like a creek or river. Temperature can drop by as much as 10F simply by going down to the creek bank. Can store beverages and food in a cooler in the creek to keep them cool for relief from the heat. Can build basic swamp cooler along creek bank and keep a small space like a tent cool.
Wear a large hat. I have a large straw hat like you see people wearing when they're working in rice patties. Keeps the sun off your head and neck. If you can keep your head cool your body can get rid of the excess heat better.
Force yourself to work in the heat for a few weeks. After awhile your body will adjust and you'll feel comfortable in temperatures in the 95+F range. Only issue is once your blood "thins" and you become used to it you'll feel like you're freezing come winter time. I'm all screwed up in this way and no amount of exposure to cold will undo it.
Wet a rag and keep it around your neck during the day. Change it often. You want lukewarm - warm water. Never sock your system with cold/icy water if you're working in high heat. You can pass out from the shock and hurt yourself. Seen it happen more than on
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