Learn how to do a simple back hand stitch, and sew a button. Just these skills alone can help you keep your clothes in wearable condition longer. Teach them to others in your family, too, so that they can carry this skill.
All you need is a needle and thread (and button if you're sewing one). The back hand stitch is great for repairing holes or split seams. You can learn more advanced hand-stitches, but these are probably the two basic ones frugal-minded individuals should know.