Which detail from "To Build a Fire" best supports the idea that the real Yukon prospectors tried to prepare themselves for the cold weather?

I would say the detail that experienced prospectors first of all would not travel in such extremely cold weather as this cheechako did and if they did at the very least they would have a face covering ie what we now call a balaclava to cover the cheeks, most of the nose and throat to prevent serious frostbite there.