Hmmm. A lot of what is possible/available will depend on the nature of the apocalyptic event, the local infrastructure and how the locals responded. I live in the midwest and we have a lot of coal fired/water cooled power plants around here. Assuming they survived (i.e. they weren't bombed) they could easily be fueled by local coal deposits- high sulfur content but it would burn well and the old mines are pretty close to the power plants. The machine shop at the plant (and some local machine shops) would be good not only for maintaining the turbines for a while but for "building down" to an early tech level that would be easier to maintain.

Agriculture is pretty similar if you have a good source of power (coal, hydro) you can make alcohol and convert older farm equipment to use it. Not dropping all the way back to horse drawn plows but maybe to something like Farmall H or Ford 8N (pre computer controlled engines).

General implications of this is you could probably have pretty decent standard of living in your 2050 world but it might look a bit like a distorted version of the 1930's or maybe later. Knowledge would be available or easily recreated since we have a solid tech/science starting point and know what the end result looks like.

Sounds interesting.

- Eric