Have a fun run or a full fledged Triathlon. Conduct it with walking distances so less serious athletes can also participate. Give out apples, or donated prizes from area businesses. Work with your local humane society and show off some of the pets available for adoption. Maybe you can find a way to turn this into a fundraiser.
Students can bring their pets.
Have a talent bazaar. Everyone comes dressed as their favorite famous person, from presidents, to entertainers to other historical figures. Give prizes for the best impersonators. Hold an outdoor concert featuring local performers. Have a big barbeque.