Ask HN: What “seeds” can I plant early and reap the benefits later?

Recently, I was pleasantly surprised by a small investment portfolio I created years ago (and forgot about), which has grown nicely over the years. It got me thinking, this is one of the things that, simply by knowing it and putting just a bit of an effort, one can reap the benefits in the years to come.

What other things should I start on early and let them grow "for free"? A few things come to mind:

Planting a tree

Investing early and properly

Learning a language

What else do you recommend?