Your most useful tool that's not a tool
 

On and off for over 30 years I've made use of a long piece of steel pipe that started life as the outer part of a 3.0 Capri steering column.

If ever I need a bit more leverage on a ratchet or, more usually, to loosen wheel nuts overtightened by Kwiktwat, this magic bit of Ford tubing does the trick.

What non-tool item have you become reliant on over the years?

I used to do the same till i broke the teeth on a few ratchets lol.

A mate called Glenn.....

I'd say a laptop computer.

Read a fault code then come indoors to research it using the laptop, then get bored and look at boobs again using the laptop