Skagway - We did the adventure park zip line excursion. We enjoyed it a lot. Fewer lines (and less expensive for it) than the Mammoth zip line, but still a great experience.
Juneau - we took the bus from the boat over to town and then took a public shuttle bus from there to the Mendenhall glacier. It was so beautiful. A great place to explore. This was one of the highlights for me personally out of all my port experiences.
Ketchikan - we walked to Starbucks in the Safeway so that I could add to my collection of Starbucks mugs and get the Alaskan one.

It was the only Starbucks on the trip that I could access easily from port. I didn't get a good impression of the city compared to the other ports we visited. It seemed like the air was more polluted and the buildings hadn't been very well taken care of. We were glad for the sun though.