I found the food tasted fine, but was not at all healthy (french fries, frozen vegetables). When I was at Mary's we had a salad bar for lunch as well as dinner though (but less at lunch). I ate at Trevs a couple times and found it was slightly better there. All Colleges have the same menu though (except 1? but I forgot which), so if you are specific about your food expect to be cooking it yourself (waste of money though!).
You are def expected to work during the holidays, but at home; you even get kicked out of College unless you specifically, and well in advance, request to stay. And sometimes you will be appointed a room at a different college in that case. They use college rooms for conferences over the holidays so students are generally banned =P