Lunch usually once a week or so, occasionally twice. Dinner usually a couple of times a month. Cooking is not a chore for me, it's my therapy, so eating out is seldom because the cook's on strike, not that that doesn't ever
happen, but... But we do eat out with friends from time to time, or hear of a new place we'd like to try, or decide that getting dinner before some event is going to be too much of a rush and we'll grab a bite on the way home, rather than getting into cooking and cleaning up at bedtime.
ETA: Oh, and fast food has a place: when the alternative is no food.