A rice cooker, the cheapest one I could find, with a single switch. Rice is now something that happens while I do something else, instead of something I stand over and ruin.

Before I got one, this sorted out most of my stovetop rice problems: https://slopslack.example.fruitful.app/weeknight-table/p/mushy-rice/

But yes, the one-switch cooker is the correct answer for most people.

Foam earplugs, the box of fifty. I live above a bus stop. My sleep improved more from those than from anything else I've tried, including the expensive things.

Seconded, plus a sleep mask. Together they cost less than lunch and turned a bad bedroom into a fine one.

A bench scraper: a flat piece of steel with a handle. It moves chopped things from board to pan, cleans the counter and divides dough. I use it every day and it cost $6.

A second phone charger, left permanently by the bed. Sounds trivial. It ended years of hunting for the one cable every night.

This is exactly the kind of answer I was hoping for. Boring, cheap, permanent.

A key hook by the front door. I lost my keys roughly weekly for my entire adult life. A $3 hook and a rule that keys go on it ended that.

The hook is the cheap part. The rule is the expensive part.