If, toward the end of my life, I were asked to write a letter similar to that which Thomas Jefferson was asked to write for Thomas Jefferson Smith, here's what I'd probably send...
Build strenuous exercise into your daily life. The human body evolved under the assumption it would be subjected to daily strain. In my era, the most efficient way for most people to accomplish this was to bicycle to and from work. That may still be the case in your era.
Automatically distrust any form of advertising. In my era, millions upon millions of women (and to a lesser extent men) who had absolutely nothing to be ashamed of were induced to feel ashamed of how they looked, for profit. Presumably advertising will become even more effective, over time, at making you feel bad about yourself for profit. Minimize your exposure to all of it.
Stay up-to-date with the basics of science and politics. Richard Feynman, who won the Nobel Prize in physics during the last half of the century in which I was born, claimed that unless you could prepare a freshman lecture on a topic you didn't really understand that topic. Distrust anyone who claims the modern-day is beyond your comprehension: even if details are not, the broad strokes should be.
Look for beauty in that which is designed to last for thousands of years. In my era, the Long Now Foundation carried this standard. In any era, humans viscerally respond to creations of lasting value.
Don't pursue money if what you really want is status. If you actually come up with a worthwhile idea in the for-profit sector, you'll find venture capitalists. If you actually come up with a worthwhile idea in the non-profit sector, you'll find donors. Neither will happen if you spend your life chasing personal wealth to the exclusion of all else.
If in doubt, get another degree. Money doesn't last until your death. Degrees do, no matter how you may get them. Plus, people getting a degree tend to be more supportive of idealistic goals.
If you're out of degrees, perform an act of kindness. If you genuinely can't go any further in education, and you still have no unique idea as to how the world can improved, make someone else's life better.