Divide Beavers into 2 teams who race against each other in a relay
One member of each team walks/runs as fast as they can to a specified point and back to their team with a book balanced on their head. They can't hold it on with their hands. If the book falls off, they have to start again. Once the member has successfully returned to their team, the next person in their team sets off to do the same thing and so on until everyone in the team has managed it. The first team to have everyone complete the task wins.