Badminton Team Small Get-Together!?

Our badminton team is going to have a small get-together since we don't have a game that thursday, so on Friday me and my friend are in charge of planning a little party. It's going to be after school, and we have very limited rides, there is a park near our school, or we can use the gym that we play in. However, students are responsible for funding themselves if we go out to lunch etc, so what would be cost-effective and convenient to do on a friday afternoon? If you have any suggestions, please tell me, we only have 1 week to plan this thing out.