Jews under Charlemagne in the 8th century and the Carolingian emperors were accredited food providers in addition to providing wine for Christian mass. I am looking for halachic responses to these opportunities; e.g., food issues, basar b'chalav, and issues of providing wine used in a religious ceremony.
It is forbidden to derive pleasure/benefit from wine that a non-Jew touched since we suspect that it may have been used in an idolatrous ceremony (not so much the case nowadays, but we maintain the issur.
We learn from the Rema (Yoreh Daiah 123:1) that one cannot give wine, which can become an assar behana'ah, to a non-Jew as a gift, since the gift generates goodwill and thus benefit is derived. I think it's fair to apply the same logic to selling wine to a non-Jew which generates profit, or at least revenue.
See more at Chicago Kosher;
Charlemagne was a Catholic Christian. I believe that the overwhelming opinion in Halacha is that Christianity is a form of Avodah Zara.
Providing wine for religious ceremonies is a form of sustaining Avodah Zara, something that is strictly prohibited. (Maseches Avodah Zara)