If you have a lake at your girls camp - here is a fun idea to do while there:
Buy rubber duckies. On each one write a YW value. Sling shot them into the lake. Have the girls paddle around the lake collecting these ducks - trying to get a complete set of the values. Hand this complete set off to a leader and try to collect another set. If they find a duck with a value they already have, toss it back. See what age group or ward can get the most complete sets.
There are several places to buy rubber ducks. Here is one website I found - CLICK HERE.