Perhaps a more simple regret, but not buying bitcoin when it was at ~8USD. In hindsight it would've been the easiest way to not have to think about money anymore for the rest of my life.
Yes, there was Bitcoin, however there are always millions of investment opportunities that may or may not pan out. Most don't.
I'd say just throw in some pocket change in places where you can afford to lose. You never know as the downside is nearly 0, the upside is in millions.
I did find a fractional BC on a thumbnail drive in an EOL software wallet for which I had long ago forgotten the password. So that could have happened too.
In hindsight...
If I had plugged that machine in, I would have probably retired by now. A few months of mining back then was enough to have life changing amount of BTC today.
I console myself in the knowledge that I'd never have kept the coins long enough for the dream to play out.