Expensive shore excursions of the town were a waste of money. Get a free walking tour map and walk the town. It can be done in 2 hours or less. Take the free bus out to the Totem Heritage Museum and Salmon Hatchery.
We rented a car and did the Mendenhall Glaciers on our terms and time. We were able to hike out to Nugget Falls and back in two hours. Most organized tours gave you one hour- which is not enough time for the hike. The downtown area of Juneau is walkable.