I suggest bring a lighted travel alarm, a night light, a heavy duty extension cord, a steamer, a blow dryer and a few 2 liter bottles of soda.
The rooms get pretty dark, so the night light will keep you from brusing your toes while walking around in the dark. The lighted travel alarm will keep you informed as to the time, plus you can set alarms as reminders. There is a shortage of electrical outlets on most ships, so an extension cord is a must. I'd suggest a heavy duty one for blow dryers and curling irons which draw a lot of current. An extra compact blow dryer is nice if you're both getting ready at the same time.
Obviously, soda is expensive on the ships, so hit a store up in the city that your cruise originates from and bring some soda along. A clothing steamer is also nice to remove the inevitable wrinkles that your suitcase put in your nice clothing.