I feel like a container factory would be a sensible thing to be vertically integrated: raw steel (or iron and carbon!) in; containers out; screws and bolts and any other needed stuff getting made during the process out of the same raw inputs. A lot like how IKEA's operation works (i.e. basically a vertically-integrated sawmill), but with metals.

That approach doesn't vertically scale very well, but the techniques from it could be horizontally scaled pretty easily across a number of industries if well-known. This is what I was on about with the hemp sacks: every industry did used to make their own hemp sacks. It was easy, and the techniques and requirements were well-known, so every business that needed sacks just did what was necessary to make them, comparative advantage be damned. (Sort of like how every large factory today has its own machine shop, or how every modern building has its own internal water-treatment+recycling system.)