You may not have to organize your own scavenger hunt. We were on the Serenade of the Seas in October, and they had two scavenger hunts organized by the ship. Ours was a 15-night cruise, so if yours is a 7-night, they may only have one (or none). Check with someone on the Cruise Director's staff when you get onboard.
Serenade of the Seas b2b January 2016