A slew of years ago, my dad bought me a Leatherman, which I promptly put in a drawer and forgot. Fast forward a couple years, and I needed to hack on some wiring at work, so I put it on my belt.
Of course, I used the damn thing throughout the day. When you don't have tools, things just slowly accumulate in a state of broke. Since it's an incremental process, you ignore / don't see how broken parts of your world are.
A leatherman is now part of my Everyday Carry. Which means much less Broken in my life. Certainly not zero, and since humans are the consummate tool-makers, we have a huge number to possibly evaluate.
Of them, which bring outsize gains given the cost?
Having a way to manage communications ( inbox zero with todo + archive, no TV, ignore any phone call from an unknown number and wait for the text ); a method for managing time ( planhack ); good friends, loves, and family; and a philosophy that helps you rank all the alternatives for any given decision, all of these seem to punch well above their weight.
Things that I should try for a bit since I see other people doing them and for which I can imagine a couple plausibly profitable cost/benefit scenarios: