1. Sunscreen, even if you have darker skin. Remember to put sunscreen on the tips of your ears, the back of your neck, the backs of your knees, and the tops of your feet if you have sandals or flip flops.
2. Light weight clothing, cotton is great. Cover your shoulders, though.
3. A hat, and don't go for style. Something with a brim all the way around.
4. Walk in the shade whenever possible.
5. TAKE FREQUENT BREAKS. We eat at QS restaurants (Disney's version of Fast Food/Counter Service), but even sitting down outside in the shade, with a cup of ice water and a chance to be off your feet, will help.
6. Indoor attractions are your friends. Carousel of Progress, shows, even wandering through a shop; anything to get in the AC to cool off.
7. Cold snacks, and sit down to enjoy them.
8. QS restaurants will give you free ice water.
9. Take a break on a shaded bench.
10. If you start to over heat, chill your forehead and neck to help cool your brain.
11. Drink enough ice water that you're using the bathroom frequently. It means you're hydrated AND it removes heat from your body
12. Air conditioned lines still count as air conditioning
13. Make use of water features - pools, water rides, cooling mists, etc
14. Portable fans can help
15. The rain can be anywhere from irritating to miserable, but it does often cool things off a bit
16. Reapply sunscreen. Follow the directions on your package. Get sweat proof stuff. I don't like the sprays, I don't think people use enough of them to be truly effective. Get the lotion type.
17. If you're the type to take a break in the middle of the day, it's a great plan. 1-5 are the hottest hours. My family refuses to do this, so we do all of the above instead.