Chamois Shirt - Gander Mountain
I have not found a better shirt for cool-weather camping. These things keep the breeze off you and shed water so well I often don't bother getting out the rain gear during rain showers. Even when it warms up, they never seem too stifling. They're tough and comfortable and I can wear one for a week-long trip and be happy. I'm convinced it's some sort of miracle fabric that has slipped under the radar all these years.