only thing i regret spending a lot of money on was when i got new rims/tires, dropped my car, put a new grill and hood on it ... and it was a 1997 2.0L Jetta. such a waste of money.
however all of the money i spent on it was earned selling vcds of family guy and band of brothers on ebay lol. i would sell complete sets daily, sometimes multiple times a day, for $40 - $50. it was A LOT of time too because this was back when like 4x or 8x burners were the fastests, and each set was like 10 or 13 discs i think.
probably made over $5k in the summer before getting banned from ebay. really wish i had used that money on something else when looking back, wishing i had traveled when i was that young too.
that is actually the one regret i have in life - not traveling when i was younger. i started at 24 and wish i had started when i was in highschool or college.
EDIT:
i also did spend A LOT of time with video games, especially in my teen years. i did not however spend much money as i was pirating a ton of games. for playstation, dreamcast, xbox, ps2, etc. i did it all and modded tons of systems. i got the point that i was more about collecting games than actually playing them though, which is when i realized i had to stop pirating and haven't done so in a very long time. i had over 1300 playstation games at one point, and i didn't really even play any of them.
i also don't regret it though because gaming is what sculpted what i wanted to do with my life and is why i got into computer science, and it's the reason i have the great job that i have now making good money. video games are also the reason i got my first job at 14 - i needed money to buy an n64. i had that job and worked from 14 - 23 through highschool and college.
i also think that the competitiveness of video games helped me with discipline overall because i just don't like losing and want to learn from my mistakes when i do lose. to this day the main form of competitive games i play is fighting games, and that is literally the only genre of game you can play where if you lose, it's 100% because you were outplayed. there are really no variables that you can put blame on. i also like the mind fuckery that comes with it, because at the advanced levels, you aren't playing the game really, you're playing your opponent and trying to get them to do what you want them to do so you can punish and beat them.