I am not GF, but I do have multiple food allergies, including milk. Primarily because of the milk allergy, some of the things I end up getting as food when cruising is also GF (muffins, donuts, some rolls).
One thing I have found helps tremendously is having that you are GF noted on the reservation by contacting special services. When
DCL knows in advance they can better prepare. Also, your wait staff will know you are GF, and when you eat at the MDRs for breakfasts and lunches, the staff there will know because it is printed on the receipt-like paper they print when you arrive.
I also go and speak with the dining staff on the first day during the "change your dining" time (e.g. Royal Court ~1300-1530). On two of our cruises they have had me pre-order the first night's meal there, the last two they did not have us do that.
Our last two cruises (B2B on the Dream) we always pre-ordered breakfast and lunch. Our wait staff would let us know where they would be, and while we didn't always choose that restaurant we often did - regardless of the choice, we decided "X restaurant for Y meal" and knew the hours that restaurant was open. Pre-ordering made things go so much smoother most of the time. And it meant I could have Mickey Waffles !! (I was told they were not available if not pre-ordered). A couple times they took longer than I would have expected to bring the order, but the head server at the meal solved that pretty quickly once he realized I was still waiting for food.
Finally, each night near the end of dinner we pre-ordered dinner for the next night. I woudl look the menu up on the DCL smartphone app beforehand so I had a good idea of what I wanted, which made the process a little quicker. Sometimes I would order something we had had that wasn't on the menu -- e.g. I realy like the butternut squash soup and we had that a few nights even though it was only on the one menu

Pre-ordering not only things like that possible, but gives them the time to do things like safe marinades and such if needed -- they basically have about 22 hours to work with.
Finally, for me at dinners the fall back is always the "lighter fare" menu, either the chicken or the steak. If nothing on the menu appeals to me, that is what I get. I might get a soup from the main menu and then the lighter fare and then a dessert. MORE than enough food. On our last cruise I think for dinners I was pretty much eating mainly form the lighter fare menu.
For desserts, with my allergies there is only so much they can do and I am fine with that. Fruit sorbet and dairy-free ice creams were available. Fruit was always available. And they often had a chocolate mini-cake with some kind of sauce and often fruit or safe ice cream. The first night they made it for me on our B2B they actually brought me the box of the cake mix (Namaste Foods brand:
http://www.namastefoods.com/products/cgi-bin/products.cgi?Function=show&Category_Id=4&Id=20 ) and the DF ice cream container to have me read the ingredients to make sure they were ok. I knew they were as soon as I saw the box, but read the ingredients just to be safe (a good food allergy practice, since ingredients DO chance even on things that used to be safe).
SW