Das ist ein Schiebedeckel...den 4-Kant frei zu legen ist die einfachste Aufgabe. Das hier hilft in der Zukunft: https://smile.amazon.de/dp/B005WSR44U
Zoom mal rein...das ist ein Schiebedeckel...einfach hochschieben...4-Kant-Schlüssel rein und Fenster schließen.
I have a a backpack for LD (various MIDI interfaces, USB-DMX dongle, laptops, AA Maglite) or a Bum bag for more hands-on electrics (where I say Knippex, Lindstrom, Fluke. And Maglite.). And a toolbox with the all important hammer (nicknamed "sweetness"), big-ass wrenches and so on.
I try not to forget this, ever.
Also a Wera of sort, but damn this one is elegant, I wasn't aware of it.
That thingy when used responsibly is a huge help, but do NOT use it as a safety controller.
Speaking of which, I tend to get people mad by insisting on using this before starting actual work. 400mA diff NOT working anyone? It happens.
Looking at how things are organised here, I couldn't get it in one bag; long jobs end up filling my car actually: Gels, and spares, and backups, and adapters, and an actual toolbox... And the cordless drill... when I do festivals or street theatre or such, my car end up the Tool-chest, you can't possibly carry it all while on the move, but you can organise your trunk so that everything comes easily at hand.