Having done two tours in the Gulf for Desert Storm in a 130F engine room on a ship, here's my advice:
1) Start sweating before you ride...you don't want to find out you are getting heat stroke after you are on the bike. Put your gear on & see if you sweat. How do you get heat stroke? If you are tired, dehydrated, just woke up, etc. Your bodies systems just haven't gotten going yet.
2) Drink, drink, drink again....stop every 20 mins to air out the crack (in the shade), and drink a pint of water. In 90+ heat, you lose about a gallon an hour. Wind evaporates more water from your skin than just standing around...multiply by 70 mph and you do some serious evaporation.
3) If you aren't stopping once an hour for a pee break, you aren't drinking enough. If it doesn't come out clear, you aren't drinking enough. If you drink a gallon an hour and still don't pee for 5 hours, you aren't drinking enough.
4) Don't drink frozen or near-frozen water in the heat. Stomach cramps will make you throw up that precious water. Thaw the frozen bottle by putting it under your jacket, but not against the skin.
5) Faucet handy? Soak your t-shirt, then put on your riding jacket. Nature's air-conditioning.
6) Getting groggy, or slow, grey at the periphery of your vision, making mistakes, feeling tired? You either have hypothermia or dehydration...
7) Don't drink...nothing dehydrates you faster than making your liver use up all of the water in your body to process out the alcohol. You can have a beer when you are done riding for the day, and it tastes even better then