Pack a couple if you like wearing them. Bring at least one to three weeks worth, since doing laundry is often expensive. Women, remember that bras are often absolutely necessary in some cultures. Lightweight thermal silk is best if you're headed for northern climates. Can also be used as pajamas.
Flannel comes in very handy in many non-tropical climates.
Other Essentials Remember that electric currents abroad are different cycles than the USA, which is sixty cycles. You may be able to sell them before you return to the States. Battery driven appliances are also fine. Remember, appliances add weight. Most seasoned travelers know that appliances easily become a nuisance - and they simply don't take them.