Ivy G asked:
He uses one at bedtime and says he can’t sleep without one. They are the size of a suitcase, but lightweight. Will there be any problem with him bringing this onto the ship and using it in the room?
How much luggage can each person bring on the cruise? We are driving down, so we are not limited by airport limits on luggage.

You need to check with the cruise line or your travel agent. Those are specific questions and different lines have different policies.
Probably not because of the risk of electrical overload and extension cords. However, ask the cruise line directly! If you have a cabin with a veranda you can leave the door open part way all night if you like.
You can bring as much luggage as you want.
But be advised, it will ALL have to be checked by Customs prior to boarding and disembarking, so that may cost you some time.
As to the fan, doubtful.