Until last week we were allowed fish. I think we are currently allowed olive oil and wine (my wife keeps track for us). Starting the 20th, it's just vegan fare. The 24th is no food or water at all, for those who are able.
That said, we are warned against being "Holier than thou." I have no idea what disciplines the monks follow and it is really not my business.
I have heard stories of monks eating meat whenever visitors arrived, both to show hospitality and so it does not appear they are showing off their ascetic practices.
Thomas Merton mentions this practice in "Wisdom of the Desert".
Thanks Martin for explaining the complexity of the fast rules. I’m not sure about New Skete, but my grandmother observes the Gregorian calendar too ... so her Nativity fast starts later and goes to January 6. I thought I read somewhere that they (like Grandma) were Russian as well ... at least the roots of their monastery.