So, assume for a moment that all women really go with it and don't have sex before marriage.
Who do men have sex before marriage with?
If you went 'ew', you have your answer.
Vegetarians belonging to traditions that make food offerings offer vegetarian food.
Eat whatever you want with whomever you want, as long as nobody is scandalised by that.
Praying before slaughtering doesn't make the meat a sacrifice. The sacrifice offered is the work.
Eating halal or kosher food won't make you a Muslim or Jew any more than non-Christians become Christian because someone else says grace at the table.