I've done glacier trips in past on small boats, including Glacier Bay and Kenai Fjords, and I'm going on a cruise this summer. I get cold easily, and I'm planning to bring a heavy winter jacket, plus a lightweight puffy jacket to wear underneath, also hat, gloves, long underwear, fleece sweatpants... mind you, I get cold easily. When you're cruising the glaciers you're crusing in a large freezer, and there's like to be wind (maybe rain). Something like Galcier Bay is a several hours, so the way I look at, I want to have enought layers to enjoy standing around in an open, windy freezer for several hours. Now, you also have the option to go inside to warm up, but I'd rather maximize my time outside.