Congratulations on your anniversary. We love sailing Alaska and have been lucky to visit 5 times in different months and can't wait for August to sail again.
I hate lots of luggage so we travel with carry-on only, a 22" roller bag and personal item each (last trip was 22 days including Iceland and Norway). Best tip is lightweight layers - tee shirt, then a long sleeve wool shirt plus a top layer of either fleece or raincoat worked everywhere except at the glacier. There are many inexpensive puffer vests and jackets that roll into tiny bags, work great for travel. For shoes we wear waterproofed walking shoes/athletic shoes and wool socks, never had a need for boots. In August we have hiked in shorts and had rain but never really cold days. On the ship it will be very casual and even evenings are not dressy unless you want to - relax and enjoy the trip. A swimsuit is nice if you want to use the pool or hot tub.
The long standing joke is to get your clothes together, then remove half.