Just a little common sense and you'll be fine.
I know some people like them, but I think misting fans and cooling towels are nasty and actually make things worse. It's already hot and humid and you're already sweating. Now you're going to spray yourself with water?? Sure, it's cool for a few seconds, but then it turns right into hot water, along with the rest of the existing sweat. Ugh. Cooling towels are the same idea. No thanks.
Afternoon breaks are fine if that's what you want to do, but you don't have to.
Here are the things we do, and we LOVE summer at WDW. Sunscreen. Light clothing. Plenty of ice water...they give it out free at any QS place. Do the outdoor rides in the morning or evening. Mid-day is the perfect time to do attractions with a/c. There are endless attractions that have it in the ride itself and/or queue. Philharmagic, CoP, SE (use a FP+), MS, Soarin', Tough to Be a Bug, Dinosaur, etc....you can spend an entire afternoon and only be in the heat when you walk from attraction to attraction. If you like getting wet, do things like Kali or Splash. Go to a water park, they're awesome!!!
Really, like I said, just use a bit of common sense and it's not really a big deal.