I don't know what people want to do, here is what we did on our last cruise. Everyone had a goody bag to hang on their fish. I made them for our group last time (there were only 8 or so of us). I just used two sheets of felt sewn together with a Mickey head on the front and a ribbon handle. Everybody brought goodies for everybody else. Some people brought a gift a day for everybody, some just one gift. The things ranged from glow sticks, to candy, to Christmas ornaments. I did bring a couple extra bags in case they were stolen but we had no problem, I had also brought plastic cable ties to secure them but it wasn't necessary. It was fun to come back to the room and find things in the bag.
I don't know how it would work for a group this size. Would everyone make their own bags? Would we do it grab-bag style, each family draws another family so your only doing gifts for one, then reveal who you had after the cruise? I'm game.