Several extra-base hits including a few homeruns.
Homerun #1 - working for a company which began its ESOP program during my prime earnings years of the late 199s so my holdings would be worth nearly $300k, my magic number for me to retire 9 years ago at age 45.
Homerun #2 - not strictly a financial decision, but it turned out that way - my decision at age 20 to be childfree. The money I didn't spend every year, keeping my expenses nice and low while building a nice, big portfolio, has greatly enabled me to retire 9 years ago at age 45.
Triple - buying my co-op apartment in 1989. While this was just before the RE market tumbled in 1990, the savings compared to renting only grew over time, leading to the first "double" shown below.
Double #1 - using some of the market gains of the late 1990s to pay off my mortgage in 1998, only 9 years after obtaining it. This was a big step toward being able to semi-retire in 2001, leading to my ER 7 years later.
Double #2 - finding a good bond fund to invest the proceeds of the ESOP cash-out, a solid monthly income source to fund most of my expenses in my ER.
Single #1 - paying off my high-interest (~8%) student loans in 1987, less than 2 years after I had to begin repaying them. I owed only about $8,000 at the start, but getting it out of the way saved me some money.
Single #2 - doing research and buying good, reliable cars and making sure they lasted a while. The car I bought in 1992, a 1-year-old used car, lasted until early 2007. Its replacement car is now just over 10 years old and should last me at least 5 more years.
Single #3 - all the money I saved by never wanting to smoke any cigarettes.