Well... I was thinking about that. Water balloons. I just picked up this thing we need to try out. It's like a little water tank. It has the spicket on it for water balloons. Fill up the tank and then you can fill up the balloons wherever you want. Kinda expensive though. $10 for the tank thing with 250 water balloons. Was thinking if it worked slick I might buy a couple more and bring it up.
Warning though: I will pitch a water balloon or two at unsuspecting adults... Just saying. If you have robotic parts that will short out with water, you better identify yourself early!