The most helpful for the most things.
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My hook pole. I attached a hay bale hook to the end of a 10 foot pole to clean trash out of a bar screen. It's come in handy for so many other things like pulling up floats, holding open check valves...I've had people arguing over who was going to borrow it first.
My home. It's where my wife and I can be safe and comfortable - and it has room for all of my stuff!
I have a set of screw drivers on my keychain. They're small, about 1 1/2 inch long, standard sized heads with a flap part to turn them with. I use those a whole heck of a lot more thank I thought I would. I need to get a new set soon because my flat heads bent. They were less than $4.
Yes I own more useful things - like a car etc. However; those are something I use all the time and they make my life just a little easier.
My mind.
Most used - my kettle.
Most useful - my drill set. From working in machine shops I have all drill sizes (number, letter, fractional and metric) that go up to 1/2" or 12.5mm
My toaster oven. I bought it almost 10 years ago from Aldi and I use it nearly every day. Uses lots less energy than my oven (in the stove) and it's perfect size for almost anything I make that requires baking.
My pocketknife- It looks cool, I can protect myself and others with it, cut things, open things, do my nails... It's man's oldest tool second to a freaking rock and my mom is still terrified of them .