Of the basic needs for a person to live non-homelessly in western countries, food is probably the cheapest and easiest to come by from charity sources after water. But people unfamiliar with the life find it easiest to think about food, and if a panhandler mentions food it's often an advertising strategy. For acquiring money for living, there's a parallel to selling your services as a software developer, solving stupid programming games in the interview, even though 90% of your time is spent on things other than writing code :)