The type of clothing you'll choose for your high-elevation excursion will depends on how high you plan to go. At elevations up to 8,000 feet (2,438 meters), your gear choices might not make or break the trip. At really high altitudes, however, wearing the right gear could literally save your life.
If you're planning to do any climbing, keep in mind that the temperatures between base camp and summits can vary wildly. Furthermore, the physical exertion of climbing may make you feel warm when you are exerting yourself, but as soon as you stop to rest, you'll feel the bite of the cold. In general, a layered approach to clothing is best.
A sturdy pair of insulated boots with wool socks is a must. If you will be climbing on ice, you'll want to consider boots with shanks. Wool base layers under lined trousers and jackets -- with supplemental Gore-Tex outer shells in your pack -- provide flexible protection. Consider consulting with the visitors' bureau or forest service at your destination for on-the-ground advice about the conditions you should expect to encounter.
No matter what the temperature happens to be at your destination, there are a couple of accessories your high-altitude camp pack shouldn't be without.