When I'm working in the heat, I normally wear a tank top with a light weight, long sleeve shirt (unbuttoned) over it, and drink plenty of fluids. Once the shirt is soaked with sweat, it does a decent job of helping. I generally alternate back and forth between water and Gatorade through out the day. Biggest thing for me is to take PLANNED breaks. Otherwise, I tend to try to get just 1 more thing done before I stop for a break, and that ends up getting me in trouble eventually.