I just completed the Hotter 'N Hell 100 this weekend in 110+ degree temperatures. As a matter of fact, I also did the 12 mile mountain bike race the day before too. I pretty much did everything joelryn pointed out and survived.
I'll also add that if your prone to cramps like I am, pickle juice will help. Mind you that I don't like pickles. In fact, I can't stand the taste of them. But a friend of mine taught me to fill up a bottle with 5 to 6 oz of pickle juice, and top off the rest with lemonade. The lemonade will mask the pickle taste. I've also used electrolyte mix instead of lemonade. It does dilute the taste a bit, but it's bearable for me. Pickle juice is packed with electrolytes and you'll absorb it quickly.
But yeah, nutrition is the key, but don't over do it. Learn to eat on the bike and spread that 250 to 300 calories across. If you eat too fast, you could make yourself sick. You'll have to experiment and find out what foods work best for you.
Also, regarding the heat. When it got to above 100, I could feel my body starting to overheat. At the aid stations, I would get ice cold water and drench my jersey with it, so that it would retain a little water. I also stuff ice down the front and back of my jersey. When I was out riding, it lasted long enough to keep my core temperature down for about 10 miles. By the time I got to the next aid station, I was completely dry, and I repeated the process.
Good luck! When you cross the finish line, it's the greatest feeling in the world.