As a frequent cruiser, these are some of my past purchases that always find their way into my luggage and have lasted through multiple cruises with me!
I always recommend at least 30 pound hooks, but heavier is better.
DIYMAG Magnetic Hooks 30lbs+ Magnet Hook
I always pack a beach toy set for the kids to play in the sand while I enjoy the ocean.
KUBUSFLY Beach Toys for Toddlers, Sand Castle
Pool decks on ships can get windy, so these ensure everything stays in place.
Danmu Beach Towel Clips, Beach Clips, Cruise
Pool decks can become extremely hot, hot enough to burn your feet....as well as slippery, so it's extremely important to put your little ones in a pair of water shoes.
UBFEN: Water Shoes for Kids - Amazon.com
Some beaches have Sea Lice that cause itching. This sun screen can definitely help prevent that.
