Massive elevation changes result in huge temperature fluctuations, so pack layers for cold nights and rest in midday heat. Scramble safely: Only ascend slopes you can downclimb, maintain three points of contact (pack trekking poles, which also save knees), test holds, and don’t climb above others. >> Deserts
Reduce heatstroke risk by wearing long, light-colored, breathable clothes; hiking early and late; and drinking one liter of water or energy drink every 60-90 minutes when temps approach triple digits. >> Deep snow
Postholing will exhaust and dampen you (with sweat and snowmelt). Improvise snowshoes by tying 3-foot branches to your boots (stem-end forward). Travel in straight lines and walk single-file, taking turns breaking trail. >> Jungles
Stay on paths (off-trail hiking may be impossible), and use a stick to part thorn-covered overgrowth. Use your machete sparingly; go around dense obstacles and look low for game trails.