If you can, get a pair of boxers in Merino wool -- comfortable, warm and they don't take on odors like some synthetics.
I am on the hunt for some of those. I have merino long johns, which I love. Hopefully this hotter than Hades summer will end soon so I can pull them out again. I LOVE merino wool and I find that boxer briefs are a good compromise back-up to pants or skivvies. They're dual purpose in that I can use them as underwear or shorts. (Sidenote for the women in the room: They aren't necessarily practical as underwear all the time, depending on your circumstances.)
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