Most wiki pages can be downloaded for offline use. For example, this would include all of the Reference and Cookbooks sections.
The exception is Jeff Borror's for Mortals tutorials, which are only licensed for online use, see terms and conditions and Q For Mortals at Amazon. Also, admin pages such as the Special pages are generated dynamically, so should be read from the website.
The wiki is frequently updated, so be sure to check the online content before reporting any issues.
The Print/export section of the sidebar allows you to download selected pages as PDF. The PDF rendering is done on an external site, PediaPress. Note that there can be delays if their server is heavily loaded.