Teenage Backyard Party Ideas?

Alright so im having a huge end of the year party with like 90 people between the ages of 14 and 15 coming (so no beer pong or anything). The party will be in my backyard and i'm getting a DJ. So the party will be like 4 hours long and I need help thinking of some like off the chain games/ activities to do. The DJ will not be there the whole time and my idea is to fill water balloons with glow in the dark stuff and have a huge fight. I need more ideas along the lines of that. Also any ideas for decorations? Im thinking Christmas lights..