Favorite tips for a cruise to Alaska:
Bring clothing you can layer. You'll want to be outdoors with binoculars the day you spend cruising near the glacier, but it can be cold. Bring gloves and a hat, too. You may want to stand there for hours.
Also, when you get off the ship in a port, the weather can go from cool to warm, and layered clothing is the way to go there, too. Bring a rain coat or rain repellent jacket.
Be prepared to be able to read a newspaper out on deck at 11pm! The sky never really gets dark that time of year.