Learn physics, it is really useful for understanding just about everything. Knowing the mechanics of machinery is also very useful. If you're asking about physical tools, there are the usual ones: screwdrivers, hammers, saws, wrench's, pliers, etc. Learn to operating a milling machine and you can make anything. Good flashlights are really useful and last a long time and there are indeed aspects to learning to use them well (battery conservation by using momentary on buttons, color accuracy-important in medicine, colors, UV, search and rescue, note taking and book reading, etc.) Also cooking, you'll live better and longer. Some basic sewing skills and the simple tools and materials that go with it. Some sociology for understanding people. Any physical or mental (or both) discipline: Kung Fu, meditation, drawing, reading+writing+arithmetic, art, music.<p>Some things have proved to be very useful in past decades but may not be so useful in the future, like small engine repair, and possibly computer programming and electronics. Small engines will cease to exist with time, computer programming is trending towards automation and libraries, electronics keeps getting smaller with less ability to manually build and fix it, though understanding electronics from a design perspective seems likely to still be useful for some time.