Assemble a bike from parts, or fix a totally broken bike.
One bike per patrol - try freecycle for old freebies.
Puncture each tyre and undo the cables so they need fixing and adjusting
Each patrol has its own (ruined) bike and they should go about repairing it with guidance from leaders.
Oiling chain and gears
Adjusting seat height to optimal position (legs almost straight when the peddle is down)
Putting chain back on after it "falls" off
Tightening parts (make things loose - brake levers etc)
Adjust handlebar height