The buy on board food makes the inflated airport food prices look reasonable in comparison. I'm assuming BA won't try to stop people bringing their own food onboard like certain low cost airlines do. Heathrow has a good selection of food outlets and those with lounge access can eat for free.
Most short haul flights simply need a sandwich/fruit/biscuits to make them bearable. Better airlines seem to do a meal and snack on flights over 5 hours. Singapore Airlines have free snacks laid out in the galley for passengers to help themselves.
https://www.gordonramsayrestaurants....ats-on/picnic/