Take a down jacket with a hood. I found that no matter the clothes underneath....short sleeve T shirt...if I had my down jacket with a hood, I was real comfy when the wind blew and it was cold. I wore this jacket...it came down to just above the knee, when it was 60 below zero on Lake Superior....that was actual temp. I had on a T shirt and jeans. The hood had fur around the edge and it kept my face from freezing when I was on the snowmobile. Down is light weight and squashes down nicely in the luggage.
Gloves a must
Light weight plastic rain poncho with hood.
Don't forget the sunscreen.
small tube of antibiotic ointment
Anchorage can be warm too, so take one hot weather outfit...
Don't forget the Dramamine (sp?) or patch.
Take a small crisscross purse with only your money/credit card/lipstick/medication/handiwipe in packet, for when you are off the ship. You don't want a heavy bulky purse to drag around when you want to use your camera.
If you don't want a down jacket, make sure you take something with a hood.
Along with the nice dinner wear for the ship, pack your tennis shoes for time off the ship. You will do a lot of walking on land. Pack some homemade trail mix of your favorite fruits and nuts. Stick those in your jacket pocket while you are out and about between meals off the boat.
Take a good camera with extra batteries and memory card.
I worked in Alaska on three different projects and was there for several months at a time.,..different times of the year. Weather is unpredictable. Layering clothes is the best way to go. I have traveled all over the world,I learned to pack light, plan for extreme weather-hot/cold, good shoes , sunscreen, sunglasses, hat and you're good to go.
Fancy dinners with the Captain is a little different. Check with the cruiseline for protocol. Most require tie for the men at dinner, some don't care if you wear casual. Most do not approve of T shirt style for men....need a collar, the cruise line should tell you.
No matter where you go, you will enjoy the beautiful scenery and crisp clean air. You will have so much fun.