I try to stay out of air conditioned places as much as possible. I find that the more I stay in air conditioned locations, the less I can tolerate the heat. My wife turns the air on quite a bit, but if I'm home alone I leave it off. IMHO people are total sissies when it comes to heat anymore; they go from A/C houses to A/C cars (often with remote starters so the car is already cool when they get to it) to A/C stores and A/C workplaces.

I don't even carry water unless it's over 80 or so, but even at 105*F (hottest I've ridden in) I still don't do any of this "pre-hydration" stuff, and I only finish about 1/2 bottle in 12 miles. I've also ridden the whole 12 miles with no water in 100* weather. It didn't bother me much, I just drank a lot when I got there. I have no idea what the "heat index" is - I just get out and ride in it.