I have a very hard time with the heat (anything over 72 degrees is too hot!) and get headaches. I use Cyclomax or Gatorade in my water bottles. I usually dilute them with water, Kool-aid or fruit juice (or some combination there of). And, I also carry a bottle of plain water in case the other stuff gets to be repulsive. I also allow myself to slow down to a speed that I can handle in the heat. I had a bad habit of worrying more about how fast I was going than how I felt. Sometimes if I just slow down for a while (and I mean really slow down) a headache will disappear on its own. And, I find that I have no trouble reaching for my bottles if I just stop pedaling while I do it. Unless you're in a race, why make it harder than it has to be?