How to get the Twig Text extension loaded I'd like to add the Text extension: 

http://twig.sensiolabs.org/doc/extensions/index.html#extensions-install

Which seems very useful because of the truncate functionality. Any idea on how to accomplish this? 

(this could've been installed by default)
Check out the Craft Plugin documentation on adding a Twig extension with a plugin. There is no clean way to add extensions manually without a plugin, as the changes might be overridden with Craft updates.