As Bicam says- liquid Elete works well. I carry it with me to put in my water bottles if I run out of Endurolytes or Jelly Belly sport beans.

I rode in hot weather yesterday- 64 miles worth of heat. I drink Cytomax- Cranberry/Grapefruit- as well as plain water and electrolytes. No cramps either during or after. This is a fairly strenuous ride with about 3500 feet of climbing most which is in hot sun with no shade.

Hydrdating will help keep your blood thin. This will make a huge difference in your ability to ride in hot conditions. Also, the earlier in the day that you can get out for a ride, the better.