Unfortunately, due to safety and fire regulations, items such as irons or kettles are not permitted to be brought on-board.
For kettles, most cruise lines do have tea and coffee making facilities in the cabin and if not, there are facilities located around the ship- usually in the buffet area and often 24 hours.
Irons and travel irons should not be taken on-board as they are considered a risk to fire safety and therefore prohibited. Laundry, dry cleaning, and pressing facilities are available on-board most ships for a charge. A lot of ships will have a launderette facility available on-board, so that guests can wash and dry their own items of clothing. Please see here for further details.
Most cruise lines will allow hair straighteners to be taken on-board, but we advise you to check the website of the cruise line you are travelling with for a definitive answer. You should consider the voltage used on the ship to ensure it is suitable for your equipment and when finished with, always ensure you unplug any items like this and leave them in a safe location.