Lunch Communication

Eating food help you to communicate better, my ex-boss once told me.  You open your mouth when eating, which makes you say something with your mouth relaxed.  This is kind of way to break ice.
Today I ate lunch (Subway and McDonald) with my classmates between the lesson and English test.  Obviously, we enjoyed the conversation on the grass of Greenwich campus with clear sky.  So, what kind of food is the best when we meet important persons as a public relations officer?