I'm not convinced anything you could study today has better than a 50% chance of still being viable in 20 years, considering how rapidly the economic, social, political and technological landscape is changing.
Possessing knowledge, skill, and/or experience involving shelter, water, fire, and food will always be handy so long as there are any humans left alive on this planet, so knowing how to build 'shelter,' how to purify/clean/manage water, how to acquire/store/utilize energy, or how to grow/acquire/distribute food will always be relevant (to say the least!). This can be approached in a high-tech manner, a low-tech manner, or some combo of both.
^^ +1 ^^
I'm too old, and to far down my path to 'learn a new trade'. But I continue to always try and learn new things that can make me less dependent on others, or society in general. A lot of people discount the so called 'simple things', like the ability to process fire wood, how to fix the car, how to make and operate a still to make clean water where there is none, or how to grow and preserve food.
Without knowing some of these skills, you are completely at the mercy of the system. If they turned off the power today, and the trucks quit delivering food for you to buy at the grocery store... How long would you be able to survive without help. Could you even cook a hot meal on the first night, let alone a year in?
These kind of skills have value, even in (especially in) an environment that is not using official green backs as a means to assign valve for goods, and service. With this kind of trade and barter, the meek and simple people can survive.
Edited by Juthro, 12 April 2017 - 12:30 AM.