I would not have wasted years working in finanace as a cost accountant!
I would have spent more time with my dad, and taken him to Highbury for a footie game or two, and a couple of Test Matches too.
I would have bought an SVT instead of a Mystique in the first place.
I would not have looked at the "Watch the step" sign and fallen down the step in the pub ... left me with lasting ankle problems.
I would never have stopped playing football or rugby in my youth in the old country.
I would have got a mortgage to buy a house when I started my first job at 18, instead of renting for years.
Could go on, but that's the important stuff I guess.