Besides the obvious clothes, toiletries, camera, I always bring some small amount of medicine (advil, zyrtec, etc...). I also bring pepto bismol because they don't sell it on the ship (at least on Princess). I think they want passengers to visit the doctor in case it is noro which if you suspect noro, then you probably should visit the doctor.
I also pack a power strip so I can plug in all my chargers and anything else I might need to plug in as there aren't many outlets in the room.
I also bring a small bottle of Downy Wrinkle releaser.