We did a short one about 9 years ago as part of our own land and sea Disney dealy. I always get motion sickness, but even my hubby and in laws did as the waves were pretty big the first night and into the next day on board.
Consider tossing a package of daytime non drowsy motion sickness stuff in there too (something for everyone or the adult and kids versions), just in case.
Same as the poster said about sunscreen...my in laws ended up having to buy it on board (wouldn't take mine and good thing as I had to share with hubby and 8 year old daughter and had just enough to make us fine and dandy for the short trip), and it was 2-3 times as mch as my drug store package.
Think prevention if you can? I also had a small...very small...first aid type kit we ALL used for something. Bandaids for heel blisters or a stubbed toe my 9 year old nephew got, some cortisone cream for my dd eczema that acted up on her wrist all of a sudden, some benadryl when my MIL got something with a bit of shrimp in it from a buffet (she just gets rashy and uncomfortable and benadryl nips it in the bud...not a killer allergy). Antibiotic first aid gel for a little burn my FIL got when he used the community iron they have on the floors for you to prep nicer dinner clothing, even my sewing kit in a little teency box for a pants button and a sundress hook.
We were prepared and all of it fit into a small make up kit I had laying around.
I also had a little pepto tablets, roll of rolaids/antacids, earplugs, nail clippers, etc, etc. I think almost everything in there was used by one of the 6 of us on our 7 day vacation (land and sea).
We had the option of purchasing a large plastic mug upon arrival to the ship. Wonder if they still do this (remember ours was many years ago)?. They had 3 different color schemes (we had 3 in each of our family sets traveling together), so we paid the high price, figured they were take home keepsakes we could use a while as well (we still ahve 2 we use!). They were free refills on the ship anytime we had them with us (after the intial price paid). So we could get soda, ice tea, milk, lemonade or whatever of those sorts of drinks they offered with these cups.
Not sure how sanitary it was..LOL, but we did wash ours with handsoap several times a day. We also had water bottles with us we refilled for land excursions.
Have fun!