Irons in a cabins is a huge no-no due to the extreme fire danger they pose. Fire is the main danger onboard any ship and any fire hazard is strongly frowned upon. Leave your travel iron at home. Use the ones in the onboard laundry room or take a travel steamer.
Most Carnival ships have a self laundry which has an iron and ironing board in it. They are on every deck. The steward can tell you. They get pretty busy but if you go when the ship is in port you have it to yourself as everyone uses it on the at sea days. My steward could not believe I used the laundry in port. He said "nobody uses it while in port" and I said that was exactly why I went then.
Another great thing is wrinkle releaser. I simply bought a small spritz bottle at Dollar General and it worked great. I had plenty for the week for 3 of us and it did not take up a lot of room in my luggage. I bet before long they will sell that stuff in travel size.
I also learned not to take the bulky formal dresses. I have a long velvet skirt that I use different sequiened blouses with-much easier on packing and no wrinkles.
Carnival Inspiration Western Caribbean- GrandCayman, CostaMaya, Cozumel, Belize