please do not say you are l lowly. I too travel solo all the time including 4 times to Alaska.
I would say excursions are needed if not withing walking distance.
NOW, if you go to Sitka, you can walk after taking shuttle to town down by the water and follow a path to the national park and the Salmon hatchery. No charge
If in Juneau, it is a great place to walk around along the water but do take the Mt Roberts Tram up for great views. Ketchikan is also good place to walk around and I would pay and see the lumberjack show right near the port
I would say overall if whale watching, helicopter flights and other things are too expensive for you (and they are for me too) then think about my above suggestions. If you go to Skagway and do not want to pay for the train, then at least walk around town.
Lastly, if you only plan to go to Alaska once, I would save up for another year and do a cruise out of Vancouver that includes a land tour. But the 1 week out of Seattle is also nice.