I 'missed out' on the usual:
Dating during High School & the first two years of college. It's not like i've had any trouble since leaving, but i would have liked to have dated in my senior year of high school and freshman year of college.
Playing High School Sports (football & wrestling). I'm not going to say that I could have made it to the NFL, but I'm pretty sure i would have been able to play college football. But again, it's one of those things where you romanticize what you might have been.
Getting a full ride via a NSA scholarship. I was offered a preliminary interview involving an NSA scholarship where i'd get a full ride plus a paid internship and a job after graduation. I, like an idiot, spoke to an elder about it and was convinced not to do it (since it would be defense related and i woudln't be showing christian neutrality blah blah blah). I took the advice at the time, but that was the last time i mentioned anything to the elders involving my secular life.