What’s your top BIFL purchase, that might not in itself has been all to frugal, but long term, will be?

After having 5-6 different office chairs over the last 10 years, none of which I liked. I went and bought a Herman Miller Aeron chair. It’s ridiculously expensive, but I’m so pleased with it and hope to keep it for well over 15-20 years. If that actually succeed, I will have spent less money one chairs than if I hadn’t bought it.

What similar items (cheap or expensive) do you feel the same about?