I'll weigh in here, seeing as how we've experienced (and survived) major heat and long distances. It's tough, but can be done.

The main part is water. Lots of it. I mean - LOTS! We don't worry about keeping the water cool - there is no way it'll stay cool throughout the day anyway so we don't even attempt. As long as it's wet, it's good. Drink. Drink. Drink.

If it's really that hot and you're sweating buckets, you may need to replace the electrolytes you're sweating out. In Latin America the pharmacies have packets of rehydration salts designed for babies with diahrrea - they are PERFECT! They taste absolutely awful, but help a lot. We probably should have taken them more often than we did, but they taste so bad we didn't. We did, however, take them if we started feeling the beginnings of dehydration and they worked wonders. I don't know what the equivalent would be in the USA.

If you have enough water, wetting your hat/shirt/whatever can help cool you down. When you're miles and miles from the next water source and are carrying gallons of water, you're better off using that water to drink rather than wet your clothing.

Try to ride when it's not so hot and sit out the middle of the day. I know, I know - that's not always possible, but it's something to think about and aim for.

On the cold water issue - I've read somewhere that hot water is actually better for you when you're hot. The theory is that when you drink cold water, your body has to warm it up and expends energy to do so - which is not what you want. If you drink warm water, it's ready to be used and your body can benefit more from it. I have no idea if there is any truth to that, but thought I would throw it out. We found that any water that was wet was good enough.