Blankets, large towels or fleece throws are a great idea. I store them in the had in a clear bag that a wilt came in. It has a handle, so if someone needs to go, it's easy to move out. We have two plug in blankets, as described above. I also have three retired Spongebob fleece throws that always gets a laugh.
Back before the camp, I always had a big puffy sleeping bag. I got laughed at by my boys, but we boated early and late in the season, and it kept me very happy. On board for emergencies, I have a few of those metalized space blankets.