Home grown food from urban gardens. Your soil is probably completely untested, and the idea of “maybe I shouldn’t just pour chemical waste out of the window” is barely 4 decades old.
And let’s not forget that any soil near a road had a ton of lead released nearby throughout much of the last century, and that just stays there. As well as lead paint chips from buildings.
And if there was a disagreement about whose property was who’s? With no laws to settle it, it would just be determined by who grabs said property and runs off with it first. That’s indistinguishable from a free-for-all.