Custom openstack image

In short what is the procedure to create my custom image for use in Openstack, i.e. I want something like the standard rancheros-openstack.img with a few of my own files added.

You can use this directory to see how we currrently build the image:

Thanks. Any hint on how to add my own files?

What files do you want to add? All config can be done using cloud-config, and if you build your own ISO, you will have to rebuild it on every new release.