Something cold on the wrists. Loose clothing, light colors.
This next part may not be feasible for some people. Start eating more fruits and raw or lightly steamed veggies. Less fats, less cooked foods, less starches. Cooked food raises radiant body temperature. Studies show that people who have a lower ambient body temperature live longer. Animal foods are especially acidic and cause inflammation, which causes radiant body heat. They also take up to 6 hours to digest, as opposed to fruit, which takes about 20 minutes. The body uses energy for the process of digestion, which again generates heat. Also, most people will experience at least a little weight loss, or a percentage redistribution of fat cells as opposed to to cells that contribute to lean body weight. Having more lean body weight allows the body to cool off more efficiently. Eating lots of watermelon helps, and for those so inclined, it boosts libido too. Eating at least 50% to 60% raw foods will not only help you keep cool, but is also a great gift to your body, pre Christmas. Two for the price of one.
From my own experience it works; I know it works. When it was in the high 80's, to even the mid 90's, I would be comfortable, have energy, while most people were struggling, sometimes even running between 5 and 7 or 8 miles if I was training, or I just wanted to get out on the boardwalk and see the sights. And this was when I was in my mid to late forties, so I know it is not applicable to only younger people.