I do packed lunches because they are much better value, better quality, and I can control what they are eating. My 3 are allowed school dinner once a week, if they choose to - for primary school that's £1.65 a day, for the two at secondary school they need £2-2.50.
For much less than the £1.65, I can give my 3 a packed lunch with predominantly home-made, wholegrain foods, including mostly organic. I make all my own bread, cakes, biscuits etc, as well as yoghurt sometimes, and they only have crisps once a week. One of my home-made loaves of bread, that does the 5 of us for one lunch, costs approx 20p if using non-organic flour, up to a maximum of about 30-35p for the best organic flour. So maximum of 7p per person per day for the bread on the days we have sandwiches.
For me it's not just about the cost, but about ensuring the quality of what they eat and the whole balanced diet. I like to know exactly what they are all eating, to make sure it fits into the wider plan of our whole family diet.
Moreover, they love the packed lunches, they get a wide variety (not just sarnies every day, although they do love those!), and it's really no faff as some seem to think - on the days my husband needs one too, I can make 4 packed lunches in less than 15 minutes!