I am not as theme detailed with the girls clothes for the cruise as I am for the parks but I still make several outfits for each girl to wear on the cruise.
I'm sure it is not typical, but neither is it really typical for the "average" guest to dress your kids up in custom made dresses at the parks I suppose.
For our up coming 7-night cruise. I am making skirts and tee's for sail away and I made tee's and had a cool skirt for pirate night. I have a couple dresses that I made for our Thanksgiving trip that they can also wear for the cruise so they will wear those as well. We typically wear dresses/skirts most days around here so that is what they wear on the cruise too. I am in the middle of packing right now. For the 7-night cruise with one day before and after the cruise in the park, I have 16 outfits for each girl laid out. Some I made some I bought, some are Disney are some are just more tropical in nature.
But really during the day most kids wear whatever they wear at home. At dinner you will see pretty much everything from princess dresses to shorts.