How to throw a good house party?

So next saturday is my birthday and i invited about 40-45 people for a big party. the people coming are from ages 15-17 and it will all be outside. i want to throw a party that noone will forget...which is why im not allowing alcohol =p. it starts at 6pm and ends when ver everyone leaves. so before it gts dark im having about 1000 water balloons filled up, and a few slip n slides=] and maybe a wet t-shirt contest and girls mud wrestling. my frind will be a dj. and im wondering if anyone knows of fun things to do outsie once it gets dark. and maybe somethings before it gets dark too. im thinking all 40 of us could walk around the neighbor hood a little bit but idk....so please help me brainstorm=]