My Alaskan cruise is in June. I'm planning on bringing a navy blue sports jacket, dress shirt, tie ( which I may not wear) , dark pants and a pair of black dress shoes. On the casual nights I'm thinking dark jeans and a flannel shirt but I'll decide when I get on board.
I've seen videos on YouTube of Alaskan cruise formal nights and there was pretty much every type of dress, but nobody who looked like they just came in from cutting the grass.