You don't really need to, just bookmark this page and you can use it any time with or without internet access. This should work for Google Chrome, Opera, Firefox and Safari. It works best in Chrome, which supports requestFileSystem (other browsers are backed by a less-efficient IndexedDB/WebSQL store).
This was put together by @antimatter15 (Follow me on Google+!) but is built on Instaview by Pilaf, html5slider by Frank Yan, HTML5 Progress Polyfill by Lea Verou, lzmajs by Gary Linscott, and of course all the content by the Wikipedia community.
This has been tested on iOS 5, Chrome 17 and Firefox 10. It works best on Chrome.