You may just want to bring a few lunch-box sized cartons of parmalat-style milk (the kind that does not have to be refrigerated until you open it). That way you have some milk on hand if your little one requires it late at night or early a.m. before the buffets are open. Also, they're handy to have for the plane ride too since refrigeration is not req'd. Just make sure you bring them in your carry on -- once I packed them in our suitcases we checked in and they exploded under pressure in the bag. Yuck!
You may also want to read the article I wrote on this section called "Bringing the Baby" for other helpful hints on cruising with little ones.
Luisa Frey Gaynor
Family Cruise Editor