I Need Help With My Party. PLease HELP!!!!!

My name is lizzy and i`m 13 I`m having a party at the local park. I wan`t the theme to be a summer hangout. It will be from about 5:30-9:00 p.m. Boys/girls invited. About 50 guest should show up. Also just in case you wan`t to know the climate here is nice and hot. It should be about 85 degrees to 95 degrees Does any one know what I should do besides have food and music. My budget is pretty low so think of something cheap.