At the recent BASK rodeo, we made buoys using extra paddle floats with ropes tied to rocks for anchors. The goal is between two buoys.

Dunno if this is good for R2K2 - lots of chance for boat-boat contact even if you're not intentionally blocking or pushing someone. I'd rather not do that in my wooden boat.

Now, there was another game played at the BASK rodeo that might work... it was a relay race. A "baton" was passed from boater to boater for each leg of the race. What made it interesting, though, was the "baton" was a live person riding on the back deck!

I also saw some folk at Paddlefest playing an interesting canoe game. Several sponges were tossed in the water. The objective was to throw a sponge into your opponent's boat... using ONLY your paddle to handle the sponge. Once the sponge is in your boat, you can't take it out until the round is done. Winner of the round is the person with the fewest sponges in his/her boat. Now, this won't work for closed-deck kayaks, but maybe some variation of the game? Like Dodge Ball? (Of course, if you have multiple people trying to get to one sponge at the same time, there is that possibility of collision...)