Kicking myself since I sold my first car. It wasn't special by any means, but I liked it. Paid for finishing a degree I never used. Should've kept the car, as now I've got the money to have made it nice.

My first new car was a 1970 BMW 2002, 60,000 miles on it. Synchros were going, otherwise was great. Sold it because needed more room for our two little kids and because I was going to med school.
Also cashed in my Federal retirement for $1800. Duh.

OTOH no buyer's remorse at all for going to med school, even though it was my wife's idea.