The key to Alaksa is LAYERS.
Also go prepared for rain - bring at least an umbrella & poncho.
I have never been lucky enough to have the warm weather that some claim to have had on an Alaskan cruise. But, be prepared that you may get lucky. Check the weather before going.
Again, the layering helps too.
If you plan to do any tours on the glaciers be sure to dress warmly, as it is much colder up top.
Beautiful sites to see.