First of all, you’re doing it right by doing a one way voyage of the glaciers!
Specifically on Alaska cruises, I like to hang out in my room and watch the stunning scenery through the balcony doors, go to Puppies in the Piazza, eat local crab and other seafood, go out on deck to view the glaciers, and play cards in the buffet along the window to watch the scenery while playing.
On any cruise, it’s fun to go to the comedy shows, production shows, guest entertainer shows, lounges with live music, dancing in the Piazza late at night, get spa treatments, swim, watch or participate in game shows, and just relax around the ship.