Packaging or Exporting Themes and Plugins

I have installed a theme on a test site of mine to practice on. Then I started making pages for a customer as a mock up. I wanted to do a real nice mock up, so I added quite a lot of detail, pictures, plugins and made a child theme to make some CSS changes. How do I export this all as a theme(in a zip?) to use on his real site. (I don't care if I have to pay for the theme license to have on both sites.) I just know that when I have gotten a theme with demo info and plugins, I can just install it and use it. Clearly I have not touched on making my own themes, so I have know idea what to do. There are elements of this site that I would use on other sites as a base theme. Of course then changing out content, styling etc...(again...I am not trying to buck the system, I will do the right thing a pay for the license for each site)