The cpanel3-skel is the directory where you'd add your content to for a new site. Error pages, default favicon, robots.txt and anything else you'd like all new accounts to start out with.
There have been many threads on the forums asking about wanting to setup a database on a newly created account you might do some digging for, but creating an package specific installation of a sites files and database I'm not sure is possible.
I do know there is a way to get cPanel to do things for you pre or post account setup that you can read more on here:
cPanel/WHM Script Hooks
Sorry can't help more than that.