For a while, I've been urging my family to take it easy on air conditioning because, quite frankly, the environmentalists are working hard to cut us off from abundant supplies of fossil fuels required to keep the A/C going. Hence, we might do well to get used to a little wider range of temperatures than is today typical in various ways.
Ways I've recommended to my family include natural fiber clothing, learning to use fans well (75 watts for a fan is much better than the kW used for A/C), and conditioning ourselves through exposure to thermal extremes. Today, The Art of Manliness presents us with a list of ways to recognize the signs of heat stroke, and to avoid them. One interesting fact that I'd not previously known--odd because I grew up running cross country, track, and road races--is that a healthy marathoner can be as hot as 104F and still be OK.
And that's a key issue for us, really. The recommendations linked indicate that being physically fit is a key part of this, and that's intuitive because (think whales and seals) fat is a great insulator. Along with that, it's key to nourish ourselves well, especially with fluids, and then bit by bit get used to the higher temperatures.