I think you're expectations of the typical person may be a bit high. As for the actual battery issue, in most cases I'd expect the batteries to equalize in a short time and carry on as needed. Life might be reduced, but I wouldn't expect explosions or anything, since the actual voltage difference is low if they're put in correctly. Most battery operated devices, save for drones and such, don't consume a lot of power, so a simple low value resistor between the paralleled batteries might be a good protective measure.
I have an old Keithley battery operated electrometer. I think the batteries were Eveready #266 type. I opened one up (simple cardboard box) and what was inside? Two (or three) standard 9V batteries plugged into a circuit card, in parallel, with two snap terminals on top. Easy way to get more capacity and seemed to work just fine. Also easy to put new batteries in, without paying the crazy price for a new #266, about $30 each, and you need three.