How can I add JavaScript and CSS files to my own custom plugin in FOG 1.6?

My plugin has several submenus, and I would like all of them to use the same JavaScript and CSS files. I want to avoid creating duplicate files for each submenu or copying the same files multiple times under different names.

For example:

index.php?node=myplugin&sub=list

should load:

myjs.js
mycss.css

and

index.php?node=myplugin&sub=something

should also load:

myjs.js
mycss.css

What is the recommended way to include shared JS and CSS files across all pages/submenus of a custom FOG 1.6 plugin?