Nix

Kind of a strange question, but let's say that the apocalypse occurs, or at least solar flares that knock out the internet for months. What services would you need to self-host to be able to arbitrarily configure and build a NixOS based system?

Ideally, you'd point your system to self-hosted services, such as your own nixpkgs and binary cache, which get synced with public repos regularly. Is that all that is needed? Or would there be more to it? How would you ensure the cache has all needed packages? Presumably you wouldn't be able to rebuild a lot of packages without internet. Or can dependencies be cached as well?