NONE. I NEVER wear underwear, and don't own any. I haven't worn underwear since December 12, 1988: The day I honorably completed my military obligation in the US NAVY. That day, after being thanked by my Captain and Command Master Chief, I changed into civilian clothes without underwear. I threw my military white boxer shorts in the trash and never owned any type of underwear since then.
Also, I gave up wearing socks five years ago at the beginning of COVID. I just use foot-powder in the Winter when wearing my leather boots, and I wear mesh steel-toe boots in the rest of the year.