I saw an interesting article about this. If one of the main pools at Disney's Contemporary Resort, Disney's Grand Floridian Resort & Spa, Disney’s Beach Club Resort, or Disney’s Yacht Club Resort is part of your plan, you may want to consider reserving a cabana. They include snacks and drinks as a nice perk too. Otherwise, the other pools are usually very open if you're just looking to cool off and not have the extra bells and whistles.