Re: I have a rule these days.
"That bag must get a lot bigger over time ...."
I turned up at a job one day with a stationwagon packed to the brim with test equipment and didn't need any of it (or any screwdrivers). Unplugging the equipment from one outlet and plugging it into another was all was needed.
To be fair the job had been causing trouble for 20+ years and noone had ever gotten to the bottom of it - the reason I was able to solve it was because I'd arrived after 5pm on Friday to find our equipment was plugged into non-essential power (despite the label on the outlet, the circuit number next to it traced to a breaker in the non-essential cabinet) and the batteries were running down. Plugging it into a working essential power circuit 3 feet away solved the problem permanently and the sulfated battery was replaced shortly afterwards, This was very much a "kicking it $1. Knowing where to kick it $9000" job.
It ingrained a habit of not only checking the power for weird faults but where the power is coming from. I've subsequently found things like untightened grubscrews and other stupidity causing supply issues. A rubber mallet isn't a silly thing to carry in your "kit of things" as it can be used to jar loose electrical connections in the building wiring and breaker cabinets... (and is tempting to use on "loose nuts" who won't shut up)