- They have to set up coordinated effort to PRESERVE as much high tech artifacts as possible.
A tractor or a rifle laying in the open will become unusable quickly. But it would take relatively little effort to preserve them in working conditions at least for decades.
- They need to set up coordinated effort to CONVERT their artifacts for new conditions.
There would be no fuel, but even small community could convert their vehicles to use gas generators.
Chips have have limited time of live due to diffusion processes, but if you stock up some transistors, learn how to make simple radios from those, then you can have radio communication for hundreds of years with little effort.
Ammunition can be home-made as well. Black powder, potassium chlorate primers, Martini–Henry-like cartridges...
- They need to keep for themselves large TERRITORY.
Using wood for fuel would require large forests.
Herding cattle would require little effort, but large pastures.
With this for the first 30-50 years they can enjoy standards of living even higher than before The Fall.
They would keep noticeable amount of vehicles and complex electronics, pre-fall clothes and other simple stuff for 100-200 years - level of living comparable with modern.
And even centuries after they will have firearms and transistor radios, stocks of metal, etc. - level of living way above medieval.