What are things you regret buying and how much did your regrets cost you?
For me it would be $115 on a 3 month gym membership for a gym I did not enjoy going, it was a small gym with all the necessary equipment, but since it's small, when you train there during the evening all the Ahnold wannabe meatheads chest thumpers are in your face, and often inject themselves into your workout.
I now go to a larger gym, with all the necessary equipment and much nicer, less intrusive people.
$50 on a pair of shirts I have no intention of wearing.
$120 on Windows 8.1.
$60 for a copy of Black Ops.
$30 for a copy of Battlefield 3, was fun for about two weeks, and that was it.
My regrets cost me a total of $375, from October of 2010 to now, it's $375 I'll never see again but it's still a small amount compared to what some people have lost in recent years.