Would have never bought my 1985 Buick Skyhawk.
Would not have sold my 1991 Toyota SR5 coupe. When I did sell it, I would have bought my mom's 1994 Ford Tempo to use, instead of the 1993 Mazda 323 I did buy. It was reliable, but uncomfortable to drive - total base model! And more expensive.
Would have gone into a trade, and not be making less than trades people by sitting in an office, after 5+ years of a liberal arts degree...
Don't get me started on the great deals I could have gotten on muscle cars I have seen over the years, some of which are worth 10 times what I could have paid for them back then!