Frequent travelers who don't want to do laundry in the sink or pay for expensive hotel laundry services can just take along several packs of OneDerWear disposable underwear. OneDearWear is 100% cotton, 100% biodegradable, and comes in several styles for men and women, from boxers to thongs. The fabric is very thin, so they won't last through more than a couple of wash cycles, but a 5-pack of thongs is just $7.99. There are also disposable socks.
Available online at the OneDerWear shop.