What's the Word? Bee
(Editor's Note: If you prepare well enough in advance, the boys in the den that has to prepare the pre-opening activity can work on this and run it themselves. There are electives in the Wolf Book for making a game. Check for other electives that might be satisfied.)
This game supports "join the game as you arrive" players. Create a stack of flashcards with words that are written in "mirror image" of how they normally appear (like the word "AMBULANCE" on the front of ambulances). (An easy way to create these cards is to print off a list of words in large print, have someone make transparencies of them and then have copies of the transparencies made "backwards." As people arrive, they're assigned to one of the two teams playing. Have the players line up in a "math bee" fashion (pairs of players next to each other) and the flashcard presenter sitting opposite the players. As the flashcard is presented, the two "front line" players try to figure out the word.
The player who guesses correctly gets a team point and those players go to the back of the line. Make sure the words aren't too big for the boys (even frontward!).