Instead of packing a lot of bulky cold-weather clothes, do as the National Ski Patrol advises: Wear multiple layers of lightweight attire, which will trap air and conserve body heat. Travel writer Rick Steves recommends a lightweight pair of long underwear made of silk or synthetic material. Worn under your clothes, they'll keep you as warm as a heavy overcoat would [source: Steves]. Add a lightweight sweater for insulation and a thin jacket or coat as an outer shell to keep out the rain, sleet or snow [source: National Ski Patrol]. When the weather is more hospitable, you can dispense with a layer or two and stow the stuff in your bag.