Quick course in Fish Extenders:
Outside your room onboard is a message holder, in most cases it's shaped like a fish:
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Once a cruise meet thread is up and running, someone in the group will (should?) step up and say "I'll maintain the Fish Extender exchange list". That person is the center point for all those who want to participate in the exchange. The list can be as simple as DISnames/room number/number of guests or as involved as full names/room number/ages of guests/like & dislikes/allergies/favorite characters/whatever is deemed necessary to know to put together the gifts.
Then each room on the FE list (note this will not be everyone on the Cruise Meet thread for your specific cruise), makes a Fish Extender holder. This is basically an organizer-type hanging bag with separate pockets for each person in the room:
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They also make up gifts (either individual gifts or room gifts - whatever is decided by your group) to be delivered during the cruise.
One note about the gifts, some groups set up specific delivery dates, and specify "each person gets a gift" or "only one gift per room" or (even) maximum/minimum price ranges for gifts. Other groups just say "whatever", so people can choose what/how many gifts to give. Some give individual gifts, others only one gift per room, while others might do one for the adults and separate gifts for kids. Or only gift the kids.