Pick up walking tour maps, these will give you a concise tour of the towns. All are cities are walking distance from the cruise docks. In Skagway definately get to the Park Service visitor center http://www.nps.gov/klgo/schedule.htm
Yes the tram is worthwhile in Juneau- if visability is clear. There is no point doing the Juneau trolley tour, everything is walkable- without mobility limitations. It doesn't sound like the above has been there yet???
Ketchikan is an excellent walking city. Plenty to see and do, at min. head back to Creek St. take a look at the wonderful totems, take the funicular up to the Fox Westmark- beautiful totems out back, then either take the "married Man's trail" back down or the funicular. Excellent souveniers in Ketchikan and there is a Walmart shuttle, big Alaska department- if you want to invest the time. (good for picking up snacks/soda etc).