You can bring buckets and bottles, but balloons are banned from this year's Water Fight in Central Park. The group that has been organizing the event for the past few years issued an ALL CAPS alert on their Facebook page noting that "PARK OFFICIALS WILL FORCE YOU TO DISPOSE OF ALL WATER BALLOONS." They also ask that no one bring replica water guns (the kind that could be mistaken for an actual firearm).
So what can you bring? It's recommended that you show up with water bottles (there will be a water supply), buckets, goggles, trash bags (so you can clean up after yourselves), and Super Soakers. We'd recommend two of the latter, one for vodka.
Should you be cool with those rules, and are 16 or older, show up at the Great Lawn on Saturday at 2 p.m. for a group cool down. And please, stay off those ballfields.