That's a tough question to answer since we all have such different opinions on what we love about cruising, especially Alaska.
There are tons of things to do on the ship, including my favorite, sitting and watching nature glide by. If you gamble there's a casino. There is a movie theater, classes, sports events, tours, a library. Too many to mention. Believe me, you'll find something to enjoy each and every day on the ship.
You don't mention if you have any tours booked. Here are some port activities we loved.
Juneau: Mendenall glacier. Don't miss it. Whale watching if you love that type of nature. Walking around the town. We didn't do this but I hear that the salmon hatchery's a nice place to see.
Skagway: White pass rail was a fun, relaxing and educational trip. Or take a scenic bus/van tour of the area.
Ketchikan: The Duck tour was fun. A bit silly but fun. Walk over to Creek street and take the funicular up to the hotel and then stroll down the married man's trail.
All the towns have a ton of shopping. We enjoyed doing our own walking tours in the towns too.
You're in for a huge treat. Alaska's an awesome place to visit on a cruise ship. Happy anniversary and birthday.