We loved the White Pass RR in Skagway.
The Duck tour in Ketchikan was a lot of fun we felt as well.
You can catch a bus at the dock in Juneau for about $10 each round trip to take you to Mendehall Glacier (visitor center costs extra). Try and go there. You don't need to book an excursion ahead of time to do that. Unless of course you want to combine with a salmon bake or canoe trip (we didn't).
Also if you're not afraid of heights the Mt. Roberts tramway in Juneau is spectacular. This is also at the dock and you don't need to book ahead of time.
Juneau, Skagway, and Ketchikan are all very small towns and easy to do self guided walking tours. Just check the maps for spots you may want to see. And of course there is easy access to the many gift shops.