A college degree.
I'm not going to get into the usual complaints about college: the debt, the rising costs, the lack of jobs, etc. I'm just going to describe my own personal experience.
I went to a good school, had a normal social life, and majored in Computer Science, a field where I could expect a nice return on my investment.
I graduated with some debt but, no problem, because of my high grades in my field, I got into one of the best graduate schools in the country.
For about five years in a row I programmed computers every day. Then I left graduate school but stayed on campus, programming for various academic projects that students and professors were working on.
By the time I hit the "real" world (programming the network of HBO, the television company) I had probably put in 10,000 hours programming or more in an academic environment. Between class projects and academic-related jobs. I was obsessively interested in programming and loved learning all the nuances.
Then I left the academic world and started working at HBO.
Within one week of work, HBO realized I was so incompetent at programming that they had to send me to two months of remedial programming classes.
After that, I was about average and would come into work at 5am and leave around 7pm and work weekends just to keep up with my peers.
I ended up starting a web services company making websites for entertainment companies but I outsourced the programming to programmers better than me. In particular, I hired on the side many of the programmers I worked with at HBO. We were very successful because of that.
The most useless thing I ever bought was a piece of paper saying I had a bachelor's degree in Computer Science. It cost me about $120,000 and 5 years of my life.
NB: This is not my opinion. This post is the opinion of a mad genius called James Altucher. See more of his articles here: http://www.jamesaltucher.com/
Neteller here: www.ituglobalfx.com.ng