3d printer. I can make custom things that just can't be bought fairly easily.
My washing machine's motor went out while it was full of water. I designed and printed an adapter that let me manually run the pump that drains the washer off of a cordless drill and successfully drained the washer. (Actually, the adapter broke in the middle, but I had the foresight to print a few spares. It only took a couple to drain the whole washer.)
A lot of the other stuff I print is custom wall mounts for things. A Raspberry Pi NAS that hangs on the wall, a mount for a SAD lamp, a mount for my Nintendo Switch Joycon charging base, etc.