This forum was the first time I'd heard of any kind of abstention
Well, this only shows how limited our individual observations can be. My grandmother used to observe the so-called strict fasting on Christmas Eve, even though this was not required by any canonical law, nor by regional customs. She ate nothing, just drank some water all day, till the Vigil Supper. The rest of us were only forbidden from nibbling on meat dishes, stored in the pantry for the Christmas Day.
There was not a drop of alcohol in our house on Christmas Eve: my grandmother and mother rarely drank, and the rest of us were just kids. But visitors were always welcome during the next two days and they would bring some alcohol with them.
I cannot really explain why my grandma observed strict fasting because ordinarily she was far from being sanctimonious. This probably had something to do with her strong inner faith and personal experiences.