Smartwool socks. Without a doubt. Wool for comfort (they do NOT itch), nylon to last. super-popular with hikers.
Boxer briefs: ex-officio. Expensive but will last forever as made out of nylon. 2nd choice would be terramar: a softer feel and different fit; try one of each then pick your favorite.
I own and use all of these. Started getting them for comfort and pack-ability on 14hr flights to Asia and now slowly converting all my regular wear too.