If you're going to be creating common methods for CGI::Application, you might want to instead create a subclass Bar which inherits from C::A. Then all of your other subclasses can inherit that functionality from Bar. I did this for a C::A I wrote. This main subclass handles sessions and authentication.
For more information on how to do this, see the C::A wiki:
You should also look at the C::A plugins, they add functionality without having to subclass.