I set up my own game sort of like a Multi-Cache. Since we couldn't all fit in one car, I made it a race between 2 teams.
We gave each team the first clue with a decryption code on it. Each team has their own course but they run parallel. In other words, Team A looks for their clue in one spot while Team B is looking for their clue in a different spot 100 feet away or so. That way the two teams can interact and see when the other team finds it and so it's a race!!!
So the final spot was at "Arctic Circle" an ice cream store where the two teams could talk afterwards while enjoying an icre cream cone.
It was a blast!!! When both teams found the last clue we were both running to our cars and my friend tackled the other teams driver so it would give us some time!!! Well, they got in front of us but they turned one way and we went straight to a different way, as we all jumped out of the car they pulled up at the same time and everyone was dashing and pushing to get in the store first!!! It was SOOO Much FUN!!!!!
We were going to have an additional prize for the winners but since it was sort of a tie, we didn't tell them about it, the real prize was the fun and how it was all fair.
This was an awesome activity for anyone who plans on doing something like this. Really fun with big groups. E-mail me for any ideas if you want to try it out.