From my handbook page on d.o

This little code snippet will add the present page title to the breadcrumb. We show you how to use this in steps.

Step 1 : If you do not have a template.php file in your sites/all/themes/yourtheme/ folder, create one.

Step 2 : Copy and paste this code in the template.php file.

Most of us have more than many functions in our template.php file. Hooks and preprocess function to make our site look as good as the designer did it. In many cases where a site requires advanced theming,the template.php file gets huge. To keep a structured and clean coding style consider using file includes. This way you can have codes in seperate php files loaded into template.php during execution.

This is a very similar approach to how Drupal core calls files from the "includes" folder.

Here's the code to include files :