On the tube on the way to LHR is what gets me. Taking all the luggage through a shopping centre. I understand the OPs dilemma actually as there are certain lines of groceries that only the larger markets stock like family size Maynards Wine Gums, Curly Wurlys and because they are cheap but just as good Morrisons Wine Gums. I usually head to the Morrisons at Shepherds Bush in the shopping centre opposite Westfields, stock everything and in the morning you can get a hearty English breakfast at the cafe across the road.