Go to your Cruise Line's web-page and look up Shore Excursions. At each stop, you will find a description of the excursions offered by the Cruise Line. Most of these are not sold on the "dock, but must be purchased on board.
Local Tour companies usually sell their tours on or near the dock. Sometimes there are additional excursions not listed aboard ship. One of these is in Ketchikan - a 2 1/2 Harley-Davison tour sold only on Holland America, on the web and on the dock.
In Ketchikan, teenagers seem to love the Kayaking tours, Jet Boat or Jeep and Canoe trip, or Crab Feed (you go out on a boat and catch the crab). The Kart expedition is a new tour they might enjoy (ATV) - combined with a Jet-boat excursion back to town.
You can rent mountain bikes at the Lumberjack Show site and tour on your own. If you are in Ketchikan in August/September, you may be successful fishing for salmon from the Creek Street bridge (pole rental is $10 per hour lures included or 3 hours for $20. Children under 16 usually do not need a license. An out of state day license is an additional $10 per day.
Sorry, I can't tell you about other cities - I've lived in Ketchikan for 3 years and only know it well.