FLL offseason task?

The FLL team that 256 mentors (Willow Glen Middle School) is having a team challenge. The challenge will pit half the team against the other half of the team to compete in a fully autonomous, FRC-like match. The 2 groups can only use parts found in the standard NXT 2.0 Kit of Parts, and items such as string, tape, and other household items. So, we've gotten the rules set up, but the only problem is we have no challenge for the robots to complete. So, that's where you at CD come in! Does anybody have any good ideas for challenges? We also have a limited amount of lego parts for game pieces, so common household items are preferred for game pieces.

Thanks!