You'll have to be getting yourself a calendar with the RC holidays marked in!
Me, I keep a check too - my Rules: never go to the Migros Wädenswil on a Roman Catholic holiday and never go to the Wädenswil Swimming Pool on a RC holiday if it is raining!! There is also a holiday when Germany's shops are closed and ours are open but I cannot remember which one it is.
Hope you find some food...