I have learned to buy things when they are out of season, not currently popular, or when there is a glut on the market. This applies to clothing, canned goods, vehicles, guns, ammo, components, and almost anything that doesn't have an expiration date (and some things that do).
I have learned to set priorities and pace myself.
I have learned to research more deeply into my potential purchases.
I have learned to reload, repair and recycle.
I have learned that there is almost always a way to do what is really needed.