An add on to package.el that caches packages in a local cache and let's you use them when the network is down.
If you install this package (it's in http://marmalade-repo.org) your package downloads will be cached to:
package-store-cache-dir
which by default is:
~/.emacs.d/package-cache
This allows you to then download the packages from the cache instead of the network. This is most useful when you are on a plane or somewhere else that does not have a network connection. Particularly so you can continue to test code with packages.
Use
M-x toggle-package-store-connected
To manually turn on retrieval from the cache.