You could have a beach party, and invite a few close friends. Go swimming,tanning, etc. on the beach. Go out to breakfast, or out to eat. Go back to the beach and play some volley ball. :]
You could have a party with games-
-A game where you have to choose from a bin, and you have 30 seconds to dress in anything. (without taking clothes off, of course.) - Play a giant game of man hunt, all across your property, at a beach, in a park, etc. - Put war paint on your face, and all of you play dodgeball.