For my mom's birthday we all chipped in and bought her a slack line. What is that you ask? It's a line that is elevated a foot or two above the ground that you try to walk across like a balance beam. It's super hard, but cause for many laughs.
We bought out half the food at Chik-Fil-A and took it the park and slack lined til the sun was far gone. It was a perfect party for a small gang of hooligans without a sense of balance.