On our VM cruise in December we purchased the Xmas room decorations and it included a fish extender. We were not part of any group, but hung it out as a decoration. We received 5 pixie dust gifts from other cruisers, which we thought was awesome! And we were in room 8004 on the Fantasy - very front of the ship, so someone actually went around to spread the love, not just pass a room and drop it off on their way to dinner.
I purchased a couple dozen small gifts like pencils and princess/marvel wash cloths and randomly dropped them into extenders, or handed them out to little kids I met in the hall or waiting for the elevators.