Layers is the key! I overpacked for Alaska, didn't take a good mix of clothes and ended up buying a couple of short sleeve tees. When you are in town, it can be warmer than you would expect so that's where layers are handy.
It can be as warm as middle sixties and then as you cruise along a glacier or fjord quite cold. Gloves and a hat are not a bad thing to have either.
When I go back, I'll take my jacket with the zip out liner and definitely a hooded sweat shirt.