A little bit of mist goes a long way toward helping people cool off. If heat is a major concern, provide small spray bottles filled with water that the guests can use to spritz themselves. If you have a little extra room in your budget, you can consider renting mist sprayers for guests to wander in and out of when the heat gets to be too much to handle. Make sure they're placed off to the side so that no one gets doused accidentally. Your Aunt Shirley will be none too happy if her designer dress is soaked without her permission -- even if it is only water.