Would suggest you check Cruise Critic website. There are fantastic recommendations for arranging tours on your own, and you can be in contact with folks who will be on your cruise.

See http://www.youralaskacruise.com/alaska_cruise_port-top_excursions.html for lists of the most popular types of excursions at each of the Alaska ports.

You need to do your homework and find out what these ports are about and what may be of interest to you. There are hundreds of excellent tours to consider. Take a look at a shore excursion list, and narrow down your interests. Repost for specific details.

take the train trip in Skagway

We took the Alaska inland passage cruise on Holland America last July and went to Tracy Arm, Juneau, Skagway, Glacier Bay & Ketchikan.

I don't know if the Princess cruises offer the Tracy Arm catamaran tour. While stopped in Tracy Arm you go directly from the ship to the catamaran. Our cruise ship turned and went on to Juneau as the catamaran then takes you to one of the Saywer Glaciers and stops when you see wild life like bears on the shore, waterfalls and whales. Because the catamaran is much faster than the cruise ship we made it back to Juneau right after the shipped docked. This was an expensive excursion but both my husband, myself and several others on how the tour was worth it. It was also 5 hours so we didn't feel like doing any other tour that day. We did walk around town. One regret was we didn't have enough time to do a whale watching tour and get to Mendenhal Glacier while in Juneau. Something for next time!

We also did the bus ride to the Yukon and then the train ride back to Skagway. The bus ride was scenic and we wanted to get to the Yukon Territory again but it made for a pretty long day. Next time I'm just going to do the train ride up and back.

In Ketchican we did the catamaran boat tour to Misty Fjords National Monument. This was a long day trip there and we didn't spend enough time at Misty Fjords. I think some of our let down was we've been to Yosemite, and Misty Fjords pales in comparison. We were there on a beautiful sunny day...maybe it would have been better if it was misty!


Utahtea

We took the same cruise in July a few years ago with Princess.

We enjoyed renting a car and driving up into Yukon in Skagway.

When we got to Juneau, it was totally socked in so we didn't go out to the glacier. We just walked around town and really enjoyed their historical museum--a good plan B for a rainy day, which is pretty common there.

We kayaked in Skagway but it's also a really fun town to just walk around in.

I highly suggest you spend several days before or after your cruise in the interior. You really don't see much of Alaska from a cruise ship.

You will get all the information you could want and with a positive attitude on www.cruisecritic.com

You could also post this on Fodor's Cruise Forum.