The key word to Alaska clothing questions is LAYERING.
You want to have a number of layers that you can put on, or take off, as the climate changes, including something that is water proof.
I know it sounds like alot, and it is more difficult than packing for a Caribbean cruise, but there's a possibility of encountering everything from weather suitable to tanning in bikinis by the pool to parka weather.
There's a variety of clothing available that is lighweight yet warm. But if you're coming from warm weather areas where you'd never use it again, make do with sweaters, rainwear etc that you use at home.
If you're doing the dog sledding on the glacier, definitel a few layers, including a hoodey style sweatshirt, and gloves.