Autoloading is only for classes, you can't really autoload random php files based on one of their function names.
Your best bet is go OOP and use classes for your helpers. You'll gain the efficiency of autoloaded files only when needed, and you'll be closer to what the rest of the Laravel community does.
But if you still want to use plain old non-object php functions, I guess you could simply individually require()
all of them from start.php, but they'd all be loaded on every page request.