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. Basic Essentials Address Book - to keep the names and addresses of old friends and new acquaintances. Although most sets should work fine, some adapter sets here in the US simply will not fit plugs abroad. You may wish to buy these at your destination.