Bottle opener... One on key chain, one on my fridge, one in my tool box and one at my bar. Plus a few others around the house. So I guess that would be my top 4 tools.
iTP A3EOS super bright LED flash light. very small, 1 AAA battery and Clips on to my belt loop. It goes everywhere with me. It has been a life saver, I would be lost with out it. I don't think there is a single day I have not used it since owning it! Mine is older, one setting. New ones have 3 settings and the chain hook is not as nice. I like the older one better.
I don't want one on my truck. Modern power steering is good enough for me for that, plus airbags kinda would make using them stupid.
One of the downsides to them is that with manual steering when you hit a hole or bump the wheel can jerk and the spinner knob can smack the **** out of you.
I do have one on my tractor. Love it for that, because I do a lot of loader work.