If I have to be outside for a while in really cold weather I have long johns. But I don't have any regular underwear.
Briefs and there are several types. Both are made by Haines. I tried boxers. Most don't fit me well. My hips and thighs are too tight if I use my waist line. Regular boxing shorts with a drawstring work. Commando is an option under some conditions . .. especially at a nude beach