Doesn’t have to be a thing you bought. Just some thing you didn’t have but then once you did it expanded your scope of actions.
The first obvious example that comes to mind is a car. Plenty of drawbacks to prevalence of cars, but being able to go where I want when I want, and far away, is very transformative.
I’m interested in other examples of things that aren’t just useful, but that open new possibilities.
Usually just taking the broken piece, measuring it out and replicating it. A good pair of calipers helps.
Of course if it’s common enough, you can usually just find things already engineered for your needs.