One tool every gearhead should have and why

It's funny you should mention that. I use a paper towel and a piece of duct tape. I wish I had a dollar for every time I was in the garage and saw blood, and thought, "Where is that coming from?". Then I find a cut somewhere that I didn't even feel. I love to hear my wife tell me how unsanitary that is.
It reminds me of a time I was doing a tailgate latch recall on a customer's Caravan. I finished putting the tailgate cover on, looked down and saw fresh blood all over their tan carpet. Sliced myself open and never even felt it. I lost more time cleaning the carpet than I made on the flat rate repair