A good ratcheting screw driver. Can't recommend a specific one, I own several. One lives in the car, one in the garage, and one in my desk draw.

Ratcheting wrenches, too.

Ratchets make cool sounds and also make the quality of life of any assembly (or disassembly) project so much better.

I lost my Victoria Nox swiss army knife between a shed and a fence when I was using the screw driver attachment on it. It will be there for someone to find someday when that block of units gets demolished. I now have something more akin to a leatherman, with a set of pliers on it, and other tools in the handle. Similar function.

I have two of those two - one lives in the wheel well of the car, the other in my desk draw :D

In terms of any other objects - I can't think of anything beyond those items that, if my house burned down, that I'd be horrified at the loss of - everything is insured and replaceable - even these particular objects. I am very much function over form, and I'm lucky my wife is the same way.