I appreciate your perspective, and I do slightly disagree but I am glad you see my point. The attending or resident (I blanket call anyone higher in hierarchy "boss") offering food is actually offering you clear, protected time for 1 on 1 with them. You can go to the lunch or whatever, not have them buy you anything (or maybe just a diet coke), and just chat while they eat. Even if they don't gel with you, on a professional level they can talk with you and get to know you or have you ask questions about your performance. I would like to say that you do not have to be personal at all with any boss, however, you do have to be professional and face time is a good opportunity - especially if protected.
Plus, science supports "food-sharing" behavior as being pro-relationship if I remember correctly. It is a good thing - it isn't about the money.