I've needed a fire extinguisher a couple times.

I've needed a can of fix-a-flat and a portable air compressor a few times.

I've needed a lithium booster pack a handful of times.

I've need a socket set and multimeter literally hundreds of times. Out of anything this is what you need to keep with you at all times.

Also I have my fire extinguisher mounted to the OUTSIDE of my truck on the back rack. If anybody needs a fire extinguisher there's one right there. I really don't mind.