You're getting lots of great advice here, I'll add my $0.02 anyway
First, a list of things you may want to bring along to be more comfortable on the ship:
•Over-Door Hanging Shoe / Item Organizer - You'll see how precious your counter-space is once you get to your cabin. Organize everything from shoes to phones, keys, etc.
•Power Strip - You'll probably only have a single 110v outlet in your cabin, bringing a power strip will allow you to charge multiple phones or laptops. *Note: Check with your cruise line if you have questions about what electrical devices are permitted.
•Travel Pillow - Relax your neck while relaxing on deck, or during that 2-hour bus tour on shore.
•Laundry Bags - So you can keep your dirty clothes separate and keep your luggage clean during the trip home!
•Large, Re-sealable Waterproof Bags (for carrying wet clothes) - Bring one with you to carry or temporarily store your wet clothes or towels.
•Mini Sewing Kit - Be ready for wardrobe mini-emergencies with a compact sewing kit.
•Febreze Travel Size - Strong food smells or smoke from cigarette smokers will cling to your clothes. A quick spray of Febreze before dropping your clothes in the laundry bag will help keep your cabin and luggage smelling as fresh as possible.
•Stain Fighter - Don't let the stains set in, dab it with a stain stick to give you a better chance at washing the stain out when you get home!
•Suction Towel Hooks - The tiny wash-line and towel bars in your bathroom will fill up fast if you're swimming. Always have room to hang wet clothes or towels, trust me you'll appreciate these!
•Document Organizer - You'll be getting lots of flyers for cruise events, shore excursions, and documents. Keep them all in one place for easy retrieval!
•Small First Aid Kit - The ship will certainly have first-aid facilities, but it's smart to make sure you have everything you need to quickly treat minor boo-boos quickly. For the cabin I recommend a small kit with a variety of essentials.
•Hand Sanitizer - (2 oz, small enough to carry with you).
•Hand, Face, and Surface Wipes (travel packs) - Great for swabbing down the kids' faces after a trip to the buffet!
•Toilet Seat Covers (travel packs) - The smaller sized travel packs are very tiny and easy to keep in a pocket or purse, a must-have if using public restrooms on ship or on shore.
•Individual Sun Screen packets - Small and disposable, allows you to carry only what you need! Don't go up on deck without bringing a few packets with you.
•Wet Wipes (travel packs) - I know this is getting personal folks, but you'll want to have a pack handy when roaming the ship and possibly using public restrooms. Positively essential if you have kids.
Next, a list of things you may want to pack for shore excursions:
•Compact Umbrella or Rain Poncho - Something flat and small enough to be out of your way until you need it. Don't get caught unprepared in the rain!
•Insect Repellant - The wipe-on kind come in individual packets so you can carry only what you need and apply them exactly where you want. Bring some protection from local insects that may be carrying who-knows-what!
•Waterproof Phone/Card/Cash Case - Keep your phone and ID safe and dry when splashing around, also lets you keep an eye on the time so you don't get left behind
Don't spend too much on brand-specific waterproof cases, there are cheap universal cases and pouches.
•Hidden Money Belt - keep your cash and boarding pass safe. Wallets and purses can easily be dropped, left in taxi cabs, or worse (pick-pockets love tourists!). *Note to travelers: Keeping your boarding pass safe is essential, without it you'll have a hard time getting back on-board your ship. Don't take chances being delayed or left behind.
•Sun Hats - If not for yourself, then definitely for your kids. Look for hats that fold up small and can be tucked away when not needed, protect your little ones' head from burning.
•Large, Re-sealable Waterproof Bags (for carrying wet clothes) - If you plan on shopping after a swim, bring one with you to carry or temporarily store your wet clothes so they don't soak through to your dry items.
•Mini First Aid Kit - Even more important when on shore, you may not be near a first-aid station. Make sure it's small enough to easily fit in a purse or day pack.
•Hand Sanitizer - (2 oz, small enough to carry with you)
•Hand, Face, and Surface Wipes (travel packs) - Great for wiping off the table before the kids eat, and for mopping up the messy hands and faces afterwards.
•Toilet Seat Covers (travel packs)
•Individual Sun Screen packets - Small and disposable, allows you to carry only what you need!
•Wet Wipes (travel packs) - For the kids and for the grown-ups, sanitary condition and toilet tissue situation is usually fine on-shore at the public restrooms, but why take chances?
For more travel and cruise tips, check out my blog at CruiseComfort.com