This plugin gives you the ability to cache certain types of content in an offline cache.manifest file
http://www.w3.org/TR/html5/offline.html
== Installation ==
- Create a directory called the
cache-manifest, and save index.php and cache_manifest.php therein.
- Upload your 'cache-manifest' directory to your instance of Wordpress.
- Activate the plugin through the 'Plugins' menu in wp-admin
- Choose what types of content to cache from the 'Offline Content' link from underneath of the settings menu.