I agree that inclusion of some sort of membrane - poncho, tarp, or painter's cloth is an important part of a survival kit. However, don't forget that the local area will offer shelter possibilities that range from barely adequate to superb. Areas of the American southwest are replete with rock shelters that are superb shelters - better than any tent. Many other locales offer more limited possibilities than can achieve adequacy, given ingenuity and time.<br><br>Climbers above timberline often dig snow caves, seek shelter in crevasses, or on volcanic peaks like Mt Rainier, use the snow caves created around fumaroles - they are wet, but warm, and climbers have survived using them.