putting action/filter hooks in a different file other than functions.php

This is a PHP question rather than WP or GF...

Does anyone know how to put custom action/filter hooks in a different file other than functions.php?

I tried to put a hook function in different file (my_hooks.php), then simply include that file in functions.php, but I'm getting an undefined function error. My whole purpose in doing this is to reduce the amount of custom code I put in functions.php.

Ideally, I would like to only register the hooks in functions.php, but all the useful code live elsewhere.

i made a site-specific plugin for my sites - works like a charm and is way easier than putting things in functions.php - here's an article about it from Otto: http://ottopress.com/2011/creating-a-site-specific-snippets-plugin/

one thing to note - sometimes code put in there doesn't fire at the right times to work, so it still needs to go in functions.php. i'm not advanced enough to know WHY, but i try my snippet in my site plugin first and then if the code isn't "working" put it in functions. php.

hope this helps!