I have lived in the Anza - Berrego Desert and it gets into triple digits up north now-a-days so I learned a few things for surviving prolonged heat events.
Wear light weight and colored, loose fitting clothes. Best are cotton, open weave natural fibers like silk or linen. Spandex and polyester make you sweat and they hold in body heat.
Drink water but take it moderately, avoid downing a whole glass at a time. But water isn't enough for extreme conditions, you need other stuff so foods and beverages to supplement are melons, all the wet ones including cucumbers have electrolytes and will help keep your body temp down. Herbal iced teas are also helpful. Sport drinks are okay but because of the sugar they really aren't a good idea as your metabolism needs to stay low in the heat.
Don't make a meal of anything, just eat lightly and make sure you have plenty of leafy green stuff and veggies/fruit that are juicy. Have some starches and proteins but go easy on those until the heat lets up, you will feel better for it.
External things, evaporation is your friend, a spray bottle on "mist" to spray at yourself when you get too warm or wear a bandana or hand towel draped over the back of your neck. Put your bare feet on a wet towel, place a trash bag or something under it. Wet the backs of you knees and ankles, wrists. I used to tie a few wet bandanas around my waist and one around my neck when I was busy but needed to stay cool.
If you go out, use an umbrella or a big hat, you can burn badly in just minutes, think subzero logic - you can freeze in moments, in the extreme heat you can burn just as fast.
Avoid pavement when possible. Limit your outdoor time and give yourself a cool down period when you come back in. This is extreme stuff, don't push it.
Stay safe my friends! I'll be in it by the end of the month. 
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