When Sir Ernest Shackleton crossed the icy glaciers of South Georgia Island in 1916—the final hurdle of his 16-month epic in Antarctica—he didn’t have crampons, so he twisted metal boat screws into the soles of his boots for traction. In a similarly brilliant stroke, John Wesley Powell, trapped on a cliff 400 feet above the Colorado River without a rope, had his men scramble up to nearby ledges and pin him to the wall with long oars so he could climb down. And John Muir crawled inside a hollow tree trunk to escape the flames of a Sierra wildfire. It seems H.G. Wells was right: “Adapt or perish, now as ever, is nature’s inexorable imperative.” To learn how to grapple with life-or-death scenarios, improvise survival tools when key gear gets lost, and grade your own emergency skills, read on.