What you should know: Underwear should have the same properties as your base layer. As for socks? Formfitting and soft. Never cotton.
Our picks: The ExOfficio Give-N-Go Boxer Brief and Swiftwick Pursuit Seven Socks. The nylon-blend boxers stay dry and comfy for days. And the merino socks never bunch and are resistant to sweat and stink. [$26; exofficio.com], [$22; swiftwick.com]