Dare I admit this? Ah, here goes:
Being a nature photographer, I always have to carry a weighty load of metal and glass in addition to all of the regular supplies, and I often have to go far out into the wilderness for long periods. So, I am desperate to cut weight any way I can.
Usually, I only take one pair of clothes for the whole trip. If the dirtiness gets to be too much, I put on my raingear with nothing underneath while I wash my clothes.
I gave up on the whole underwear concept. I tried boxers, briefs, cotton, silk, polypropylene, etcetera, etcetera. When you do serious hiking, they all chafe (in the two places I'd least want chafed, too). They're tight, or they ride up--or both!--constantly, forcing me to stop and make some inimate readjustments.
Instead, I wear looser pants and use baby wipes. God, those baby wipes feel like a little bit of luxury, on a long outdoors trip. (In fact, they're an inexpensive small luxury worth using at home. You'll never go back to T.P.) They keep me squeaky clean, and they're much lighter than numerous pairs of undies. If you can't find biodegradable ones, then use the used ones for tinder.
I also wear no socks. But this only works if you also wear no shoes. In very rough terrain, such as aa-aa (jagged lava flows), I'll wear sandals. Otherwise, I don't bother with the footwear at all in the outdoors. If this sounds radical, keep in mind that most of the people throughout human history didn't have shoes. We're built to use our bare feet. I'm not necessarily recommending that you throw your shoes away: some people's feet can handle this while other's can't. But, it's worth considering. My feet are fine barefoot over rough ground, with heavy loads on my back, and down to about 20 or 25 degrees Farenheit.
Lighten your load. Free your testes and toes.