I don't know if it's beautiful, but here is one of mine.

It sets up me as a user: https://github.com/cswank/dotfiles/blob/master/nix/configura...

Sets up a hobby app I built via systemd: https://github.com/cswank/dotfiles/blob/master/nix/configura...

Defines a cron job that backs up my music files: https://github.com/cswank/dotfiles/blob/master/nix/configura...

Opens up ports in the firewall (they are all closed by default): https://github.com/cswank/dotfiles/blob/master/nix/configura...

The rest is pretty much boilerplate from the default configuration you get when starting from scratch.