We brought Cokes and Pepsis aboard the Dawn - one 6-pack of 16-oz plastic bottle Cokes and 1 6-pack of 20-oz plastic diet Pepsis. One 6-pack in each large suitcase. I would assume you could bring aboard a small (pint) bottle of rum as well, but haven't tried it.
A small bottle of rum in a plastic bottle in checked luggage should not cause a stir. The funniest thing happened on our lst cruise to St, Martten. We came back to the ship carrying our liqour purchases in a beach bag that we bought, fully expecting them to take them until the end of the cruise. They didn't, they went through xray, hanging out of the bag, nothing was said? I give up on trying to second guess them. I would say that if it appears that you are trying hide something or set up your own :"bar" they may take a look at it.
Irons are not allowed-fire hazard. We have always taken 2 small travel bottles of liquor in our checked bags for a drink while getting ready for dinner. Put them in a plastic zipper bag just in case they break. No problem! As far as the "obvious", nothing illegal, it WILL be found! Those cute little beagles love their job!
"A truly happy person is one who can enjoy the scenery on a detour."
You can order liquor for your room through room service while on board, cost is very reasonable. You can also order a bottle of any liquor ahead of your cruise as a gift to yourselve which will be delivered to your cabin the day you depart. The verification will be in your cabin when you board. Simply call room service, and it will be delivered. Go on line to Princess.com to order or call Princess. You do not have to worry about sneaking booze in your checked luggage, it will be there when you arrive. You can lso order mixes for your rum.