For my sons 9th party he wanted to do a water wars party. I wasn't quite sure where to take that until I realized he really just wanted a party that involved water and having a water fight.
I gathered a couple ideas for a fun obstacle course from pinterest etc. and adapted them to items I already had from home. Our first obstacle was carrying a bucket of water on our heads while we "walked the planks" and jumped over the alligator.
Our second water obstacle was that we needed to toss water balloons (which I filled up most before the party) into the water tubes. I had to put boards over the water tubes so they wouldn't fly away. This didn't look cute or nice but nothing blew away.
Next I used an old slip n slide, folded it in half and staked it into the ground. I used water noodles, a dollar at the dollar store with small dowels in the ends of each side. The kids had to army crawl under them.
Here I had 3 hula hoops from the dollar store and the kids had to jump one to another.
Next was the hit of the party. I used 13 bottles of $1 cans of shaving cream, again from the dollar store. I filled up our small plastic pool and had put small bouncy balls in before the shaving cream and covered them. The kids had to "dig" to find a bouncy ball. They had swimming suits on so we were all good to get dirty. (I filled the pool up about 1 hr before the party and left it in the garage out of the sun, It kept it's shape and texture just fine.)
Next was the slip n slide......
After we finished the obstacle course we cleaned off the shaving cream with the hose. And split the boys into two teams to have their water war. I filled up lots and lots (about 300) water balloons way before the party probably 3-4 early which was too early. The balloons kept popping in the buckets and just leaving water in them. I would fill them up early again just not too early.
We also bought the water balloons and water guns from the dollar store. The balloons worked great but I would buy easier to fill water guns next time. The kids had a blast, it was a little more work than I thought it was going to be once I got started but it all turned out great. For goody bags we put in an inflatable beach ball, bubbles, empty water balloons, and a water gun.