I'm a big fan of KFC, just grilled chicken + green beans + mashed potatoes. If I can dig up a coupon, it starts to reach the cost that I could cook food for at home. Always a winner once or twice a week.
Not sure if anybody else does this, but I really like Denny's in that you can order a grand slam and customize it to your liking. On lower carb days, I only eat two wheat pancakes and then do 8 eggs + turkey sausage. On higher carb days, 4 pancakes, bunch of egg whites + turkey sausage or ham and I'm good to go. Very affordable too.