I think in our culture it might seem a little strange to offer and accept food from strangers.
At least this is the impression I got one day when I offered some peanuts I was eating.
I know that I hate it when I am sitting in class hungry and the person next to me is chowing down! I was eating some peanuts during class and simply offered some to the people sitting around me. Because they did not know me perhaps they were confused or wondering what was wrong with them. I just wanted to politely share. Maybe it is the norm to politely turn down food. (Whereas in South America or Latin cultures it is extremely rude to turn down food.) I think because I have had a taste of both that I am in the middle but at the time when everyone turned it down I felt silly!
I think it is conforming though. There was one time when I offered everyone around me and everyone laughed and said no.
There was another time when I offered my food and after one person accepted, those who had politely turned my food away asked for a bite.
I think when people got more comfortable around me then they were more likely to accept the food.