I went to Alaska some years back and it was awesome!!

The tip I have for you is to stand on the deck, not stay in the boat's cabins. I took full advantage on the Prince William Sound and stood by the deck, watching mini-dolphins jump past, red / orange / clear jellyfish swim by, little sea otters on their backs, and bald eagles spreading their gigantic wings.

I think I would've regretted staying inside the boat.

The boats sell cups of hot chocolate (yummy), that'll warm your entire body up instantly. They also have these hot balls to buy that you put in your pocket and hold in your hand.

And seasick pills - even if you think you can handle the choppy water without growing nauseous, these pills can't hurt - and it's a good precaution. You definitely don't want to spend your entire trip sick!