Alaska weather is funny. You have to pack for all things, but still be sparing.
Clothing in layers: T-shirt, sweatshirt, fleese and light jacket ought to do it while letting you have flexibility to shed layers. For pants, I went with jeans and shorts (definitely made use of the shorts). Some prefer windpants for quicker-drying.
Sunscreen, hats and sun glasses. 1 bathing suit.
Binoculars. Hugely important in Alaska. We took 1 strong pair for use on the ship and on more stationary excursions (ie. whale watching). The strong pair make a huge difference in seeing otters and seals, etc. We also picked up a couple of small binoculars so that (1) the other person could look simultaneously and (2) we could both carry binoculars while in port/hiking/etc without luggling around heavy stuff.
Lots and lots of film/digital memory. Camera with a good zoom on it.