Pack high-quality, weather-appropriate clothing designed to keep you warm and dry. Layering is essential, so bring light to mid-weight layers you can adjust throughout the day. A waterproof and windproof jacket, hat, gloves, scarf, sunscreen, and mosquito repellent are all useful additions.
If you plan to hike, especially on glaciers, bring sturdy, well-broken-in hiking boots with good traction and a comfortable daypack. For camping trips, consider specialty gear such as a sleeping bag liner or headlamp.