In the rare occasion that I fly BA shorthaul, I sometimes take with me some food and drinks from the terminal (as BoB is a no go for me). Last year on the ATH-LHR, I got myself a big of food. When I boarded the plane, the CC told me I was right to bring food onboard as they might probably “light” on their M&S selection. On other occasions, I had some funny looks when Handing over my non M&S branded rubbish to the cabin crew.