We brought a tennis ball so that I could practice throwing and catching with my son. We did this in the basketball court area/hockey area when people weren't around. Also, you could do this at many of the beaches, if you stayed away from people.
We also played ping pong, shuffle board, basketball and soccer which were all mentioned in the previous reply.
The basketball court can get crowded at times, but most people are just shooting and have no problem if you want to join in.