When developing my website I called all the includes in my php files by calling one single file called includes.
The code of this file looked somethig like this: (I
Two suggestions here:
You're going to want SITE_ROOT to be absolute path of the directory your files are located in. For example, in the above code, this directory is C:\wamp\www\ArmyCreator. You can define this manually if you know the directory, or dynamically by using the predefined __DIR__ constant (PHP 5.3+), or dirname(__FILE__) if you're not on 5.3 yet.
Including a bunch of files all at once in generally considered bad practice, and autoloading should be used instead. This will give you better performance as well as a well-defined directory layout and naming scheme, leading to better code. To do this, you can use the spl_autoload_register() function.