Some of it depends on the staff involved.
A similar thing happens on weekends - sometimes the bar is open, some other times it's purely a pay per drink type scenario up the back.
I doubt if you'd get the newspaper, but you'd get the normal meals etc.
TBH, I've never travelled CityFlyer on a public holiday, although once again, I've never seen any * on the Qantas site telling me that CityFlyer on Christmas is any different to CityFlyer the day [or 2 days] before.