I think it is great to aim for self-sufficiency in your life. I think there are 3 skills that are very easy to learn.

1. The back-stitch
This is the strongest stitch you can do by hand and it works on almost everything. It is also very easy to do. I have mended buttons and shirts (the place near the collar tends to wear off easily). I have even mended my umbrella (the velcro tape part to keep the umbrella closed). I don't think I'll have to buy new stuff that often anymore.

2. Cooking
Well, just cooking edible stuff is very easy. There are also very simple dishes that are delicious and hard to screw up. E.g. soup, fried rice, eggs, sandwiches.

3. Hair cut
You have to be prepared to screw up a few times before you get it right, but after you get it right, it is very liberating. You can cut your hair anytime, into any style you like. A good pair of hair scissors isn't expensive and will last you a while (4 years on mine already).

Praise or punishment / Regression to the mean

The psychologist Daniel Kahneman, winner of the 2002 Nobel prize in economics, pointed out that regression to the mean might explain why rebukes can seem to improve performance, while praise seems to backfire.

I had the most satisfying Eureka experience of my career while attempting to teach flight instructors that praise is more effective than punishment for promoting skill-learning. When I had finished my enthusiastic speech, one of the most seasoned instructors in the audience raised his hand and made his own short speech, which began by conceding that positive reinforcement might be good for the birds, but went on to deny that it was optimal for flight cadets. He said, “On many occasions I have praised flight cadets for clean execution of some aerobatic maneuver, and in general when they try it again, they do worse. On the other hand, I have often screamed at cadets for bad execution, and in general they do better the next time. So please don’t tell us that reinforcement works and punishment does not, because the opposite is the case.” This was a joyous moment, in which I understood an important truth about the world: because we tend to reward others when they do well and punish them when they do badly, and because there is regression to the mean, it is part of the human condition that we are statistically punished for rewarding others and rewarded for punishing them. I immediately arranged a demonstration in which each participant tossed two coins at a target behind his back, without any feedback. We measured the distances from the target and could see that those who had done best the first time had mostly deteriorated on their second try, and vice versa. But I knew that this demonstration would not undo the effects of lifelong exposure to a perverse contingency.

This is why I love statistics. It applies to so many things in real life. Regression to the mean is so pervasive in our daily lives.