Just a few words of advice. If you are insulin-dependent, check way in advance for a refrigerator for you cabin. Carnival only had two cabin refrigerators for the entire ship (Imagination). I had to keep my insulin three decks uo in the Purser's refrigerator. When I needed it, I would have to leave my cabin, go get the insulin, take my shot, and take the insulin back to thte Purser. They were very nice about it, but it was disconcerting to have to stand in leach time. When I went directly up to the desk, I got dirty looks form several passengers, so I usually waited with the milling hordes. Neither my travel agent nor the Carnival people seemed to appreciate the need for insulin refrigeration. If the airlines weren't so phobic about weight and number of bags, I would have had one of the cooler/refrigerator combos that are out there. I also carry two freezer packs to keep the insulin cold on the plane and such. I had the Purser freeze them for me on the last night. Whatever you do, do not let them talk you into putting your insulin in the ice bucket in your cabin. The ice melts and water can seep into the insulin pen. I know this from experience. Also, you shouldn't freeze insulin and that is what happens when it sits on the ice long enough.
Please keep track of your blood sugar levels. Keep some candy or orange tablets handy. We had a medical emeregency when we landed in Atlanta. Luckily there was a doctor sitting directly across from the woman. He yelled for candy and I yelled for orange juice. The poor woman was having a seizure episode. I told her I had insulin and she said she had the pump. I'm thinking she might have been running low on meds because I thought the pump automatically adjusted the dose. In any event, that incident made me much more aware of my responsibility to myself. The flight attendants were concerned because she was traveling by herself. When I asked for a refrigerator, the Carnival folks made me fill out a special needs waiver and strongly suggested I bring a companion to "nurse" me. I certainly do not want diabetics to face more discrimination when doing what others do as a matter of course.
Actually insulin does not need to be refrigerated as long as it is not allowed to get excessively hot (above 85 degrees F). I work in a hospital and we do not refrigerate any of our insulin we are currently using for patients.
An insulin pump does not automatically regulate insulin levels. A person still has to test their blood sugars several times a day, and pay attention to their activity and diet. When they test their blood sugar, they give themselves extra insulin with the pump based on their blood sugar readings.
The ABC/R meds that people with MS take do need to be refrigerated. I don't know about Carnival (it is a lower cost cruise line) but on Holland America they have refrigerators you can rent for your cabin, but you must reserve them in advance. They only provide refrigerators in their more expensive cabins. Some lines such as Crystal (and some Princess ships) have them in all their cabins.