Eat more bacon. I was a skinny teenager. After I was 22 I gained a lot of weight. I'm 33 and finally discovered keto/low carb eating and it's working wonders. I recognize that I never really had the interest in doing sports growing up, so if 16 year old me kept to a low carb diet we'd have maintained a low weight through the years.
Finish college. It's a real popular idea to drop out and "do the startup". If you have a side project that gets traction AND MAKES MONEY then that's probably ok. In my case, I did a bit of school and have self-taught myself a lot. I'm really good at what I do (web development), but there are holes in my knowledge. More importantly, I'm regretting now not being exposed to other potential fields of interest like astronomy, solar power, etc. I'll never have that experience unless I show up on campus like those guys in the movie Interns. Kinda akward and I'm not that funny.
Last thing would be to seize opportunities when they come. Always say yes. I don't do that enough. Go to that party, attend that meetup. If you have an opportunity to travel, do it.