This includes the LICENSE.txt but not other files like CONTRIBUTORS.txt. It also doesn't exclude the .tox directory. Additionally LICENSE.txt isn't included in the whl file during python setup.py bdist_wheel. I have also been working on altering MANIFEST.in. This is what I currently have:

include *.rst
include *.txt
include *.cfg
include *.py
include *.ini
include regen-docs
recursive-include docs *.html *.css
recursive-include formencode/javascript *.js
recursive-include formencode/i18n *.py *.pot *.po *.mo
recursive-include formencode/tests *.txt
recursive-include examples *

prune docs/_build
prune .git
prune .tox
prune build
prune dist

Any chance you know how to include/exclude all the things?

I'm not sure about the wheel issue as I really haven't built any previously. The only thing I could find is the following stackoverflow answer, https://stackoverflow.com/a/39823590/392949, but it seems like you're already using include_package_data=True in setup() of the setup.py. So unfortunately I'm not sure. I tried to build the wheel, but examining its content, I didn't see the LICENSE.txt file either.

Maybe setting this in setup.cfg will help:

[metadata]
license_file = LICENSE.txt