There are many other tools in the Apt family that can assist with managing packages.
apt-move can build a local "installed packages only" repository,
apt-cacher-ng are caching proxies,
apt-proxy is another proxy and partial mirror builder,
apt-zip can update a non-networked computer using Apt and removable media (Zip here refers to the old 100MB floppy-like media, not the compression),
aptoncd creates CD-based repositories with packages downloaded by Apt
These are available as individual packages; for the most part, you'd install them on the machine with network access to the official Apt repositories, and use them to create package repositories on removable media (for
aptoncd) or configure that machine to be a local repository that other machines on the local network can access (for the various proxies and
As Broam points out in the comments, if you have differing architectures some of these will be more useful than others.