Frozen Food
First of all, your own freezer will produce ice that is much colder than what is commerically available. Second, blocks are much better than cubes. We make "blocks" in plastic containers when we start a trip.Third, freeze food when appropriate. We always make a batch of chili, and freeze it. Soup, meet, and other freezables for use later in the trip.With these tricks, our ice-box was still freezing the loose water in the bottom after two days of 10 day June cruise. One bag of cubes on the top was all that we needed for five days. By then only the large plastic containers had any ice left, and we were adding two bags of commercial cubes per day to keep proper refrigeration.As mentioned already, the CO2 released by the dry ice is heavier than air. It will pool bottom up in your cabin, and can be deadly.DavidLady Lillie