Cotton underpants and travel don't go together. You need special travel underwear, which cut down on chafing and absorb moisture, and providing better comfort (with better stretch) as you go places.
Good travel udnerwear are made of thinner material, taking up less space on packing. They dry much faster than your normal underwear.
Good men's and women's underwear provide a balance of proper fit, comfort, odor-proofing, and value on your trips - road-trips, hostel-hopping, backpacking, or just plain tourism.
The best underwear for travel (for men): ExOfficio Give-N-Go Sport Mesh 6″ Boxer Brief (soft fabric, long lasting, quick-drying)
The second best underwear for travel (for men): Tommy John Air Boxer Brief (Well-tailored, comfortable, extra-soft, adjustment-free boxer briefs, pricey)
The best underwear for travel (for women): Patagonia Active Hipster (light, stylish, quick-drying)
The second best underwear for travel (for women): Ibex Balance Brief (Natural resistance to odor and bacteria)
The best affordable underwear for travel (for men): Uniqlo Airism Boxer Brief (Comfortable, compact, fast-drying)
The best affordable underwear for travel (for women): Uniqlo Airism Seamless Shorts HipHugger (no-ride cut for women)