I've more or less come to the same conclusions as people who are far more spiritual, but from the opposite direction.
Being cheerfully nihilistic, I think everything happens for a reason, and that reason is randomness and the chaos of the universe, and being idiots. Deal with what comes at you the best you can in that moment, knowing you're ultimately a dumbass just like everyone else, and you'll have minimal regrets.
I'm not butterfly-effect in terms of decisions ultimately leading to your best possible life... sometimes you **** around and permanently find out... but, I also wouldn't change something 5 or 10 or 30 years ago with zero knowledge of what all it would impact for better or worse.
Probably the biggest thing though would be wishing I had put more effort towards knowing my grandparents and many extended family members more so when I was younger... I was pretty antisocial growing up and my immediate family really only saw extended family at holidays (definitely didn't come from the outgoing wing of the family). As I got a bit older, I definitely could have put more effort towards those relationships (one example, my mom had a big falling out with her mom, so I didn't see my grandmother for years growing up. I saw her while I was working at a restaurant when I was ~16 or 17 and she told me "just so you know, you can always stop by anyway"...
). Grandparents have passed, as well as some other extended family members.