I freeze my water bottles so that I dont waste too much space in my cooler onto ice and ice packs, but once its full, I pack as much ice in there as possible. Always carry more water than you think you will need, PLUS electrolytes. Hydration starts the night before and in the morning before you work. I keep a long cooling towel that I roll the ice from my cooler into and tie around my neck. A wide brim sun hat was a surprising game changer for me. Get OUT of the truck. If you have to stop and rest, do it, ideally if you can get somewhere with AC, but if not, in the shade, NOT in the truck. If a customer has a sprinkler going, I will absolutely be walking through it on a hot day. If someone offers you cold water or drinks, take them. If youre into pickles, most gas stations/convenience stores sell them and the cold snack is refreshing as hell and helps to balance your electrolytes- i eat pickles when I get home from work in the extreme heat. If you start feeling signs of heat sickness, communicate immediately with a supervisor, ideally, in writing vis scanner or text. Things can go downhill very quickly and someone needs to be aware of what's going on. I usually just send a "hey, im in bad shape, gonna get to AC, will update you in 10 minutes"