> not using image sprites
sprite_images filter: https://developers.google.com/speed/pagespeed/module/filter-...
> not using a cookieless domain for images and other static content
MapRewriteDomain directive: https://developers.google.com/speed/pagespeed/module/domains...
> not using a CDN
Once you have a (pull) CDN set up, mod_pagespeed can rewrite your resources onto it with the same MapRewriteDomain directive.
> blocking javascript - worse if it’s in the head
defer_javascript filter: https://developers.google.com/speed/pagespeed/module/filter-...
> not minifying your javascript and CSS
rewrite_javascript: https://developers.google.com/speed/pagespeed/module/filter-...
rewrite_css: https://developers.google.com/speed/pagespeed/module/filter-...
> not optimizing caching policies
mod_pagespeed automatically longcaches everything: https://developers.google.com/speed/pagespeed/module/filter-...
> not gzipping your content - most if not all popular web servers support some type of compression
mod_pagespeed automatically enables gzip compression
About half of these are enabled by default (minifying css and js, optimizing caching, turning on gzip) and the rest need to be configured.
(If I were making the list I would also have included resource combining for css and js, which mod_pagespeed does by default.)