[@Frengo]

One of the biggest bits of post-apocalyptic fiction anyways is the ruin it takes place in and feeding off the most basic of things left behind from the world before. Whether it's jury-rigging together cars in the same vein of Mad Max or Fallout where most of (or all of) society is built literally atop the ruins and the remnants of the material of the passed duct-taped together to create a usable tool. Society and humanity is too smashed for a cohesive enough society to arise to build anything as complex of high science-fiction (with actually very limited exceptions in Fallout).

It'd be a thing to pause and consider this. Though you might have "highly efficient crops" all that does is settle that there wouldn't be any wheat famines, or less of them. Not that anyone's spending any less-time harvesting and planting it.