Another way I'd think about it is what kind of community could rapidly, and relatively painlessly, integrate into a pre-modern civilization?
Like what kind of place could land in the past and start trading and doing commerce the very next day, so that it can start hoovering up food, and exporting goods, and ride along whatever existing stocks of spare parts for a few decades, as it hacks together hybrid parts to make it all work. Like... what kind of place could get jumped into the past, and start trading, so that the locals are happy to give them food in exchange for goods, and be the kind of place that can keep producing goods. Maybe need to shift to higher-labor modes of production, but that has productive capacity already there to continue chugging along.
So for that I'd like to propose as an example Frankenmnth MI, as a sort of example case; it has a lot of local agriculture, and historically it was a place local sheep-farmers took their wool to be processed. The town has since pivoted to tourism but it's still got a few places around town that take in raw wool and turn it into processed goods, such as socks or sheets. They mostly seem to be boutique/organic/"foodie" products looking at websites, which means they're going to be relatively vertically integrated and relatively low capital compared to real serious modern factories. But that's good for ISOT because when they're magically cut off from supply chains, it's not the main product line that's missing links, it's stuff that supports that main chain, so to speak. (That's how I found the town, looking for places on the internet that advertised they'd turn raw wool into yarn etc).
So you've got a place that still has some sheep, that has the direct production line to turn wool into finished goods, in a town of 5000 people. Yeah it's still got all the massive secondary dependencies (electricity, and chemicals, and so on) but because it's low tech relative to modern factories, it could probably limp along without needing spare parts for a pretty good while.
And meanwhile you can trade modern-quality socks for food with the locals pretty much immediately, and keep producing socks, and probably retool a pretty good chunk of town into a sock-and-clothing production zone, which would generate the wealth needed to sustain a modern community with extreme labor specialization.
Well the other example case I guess would be like a national arsenal (not a place that stores fighter jets, a place that stores rifles and has literally a billion rounds of ammo) that could extract what it needs by military force rather than trade, but that would get pretty damn ugly, I don't really want to think about it in depth. I bet Fort Benning could do an awful lot of conquering just with having like three infantry brigades stationed there; no need for fancy planes, and they probably already have enough ammo to kill everyone else in the world anyway. Accursed place has an awful lot of personnel scandals too, probably a good chance the officers there could talk themselves into doing a conquest bender.
