As I posted earlier:
This the sort of thing we make and support:
It's a variable frequency drive (330kW) with, in this case, an active front end.
And this is the sort of stuff I routinely carry around:
The black box is general tools, a multimeter, leads, clip on CT, torch, and things of that nature. The grey box is a fairly comprehensive socket set, and the blue box has a scope, PPE, and a few other useful items. The green box is a first aid kit, and the red thing is a fire extinguisher. I usually take my laptop too. All strapped in and all eventualities covered...
Service work comes in many flavors. I imagine if I were servicing photocopiers or vending machines I might need different things.
That said, I don't do a lot of service work. Just now and again, if the guy on call is in the wrong part of the country, or even in the wrong country, or various other circumstances, I'll take the call.
It isn't my day job.