We did the bike excursion in Skagway (White Pass train up, bike down). It was high 30s to low 40s when we started biking down and when we reached the town in a couple hours, it was mid 70s.
In Seward we hiked out to the exit glacier. Kinda cool to start but as we walked through fields we were sweating so took off our coats and long shirts - down to t-shirts. 10 minutes later as we approached the glacier we were putting everything back on again.
It's a bit of a pain but I'm sure glad we got the packable gear before we went. Warm coat, rain coat, rain pants - all pack down into their own pocket. If you want to get fancy, get the convertible pants where you can zip off the lower leg portions. Each member of your party will need a backpack to carry their own layers.
The one thing I wish I had done was to get a larger size rain coat. I wore my backpack under my rain coat to keep things dry but it was a tight fit. Other option is to get a waterproof backpack.