All sorts. It could be a Python file with a dictionary of datetimes to targets for that week, it could be a file containing an enum of our suppliers, or (less a data file) it could be a template for a page on the site.

The point is that they are code, or a file directly loaded in, stored in source control, rather than dynamic data stored in a database that needs an editing interface.

I guess aren't all files "data files"? When I think data files I think of a file that contains data points (CSV, tabular, etc).