Letter carriers in many Iowa cities will be taking part in a food drive today, and all people need to do is put non-perishable donations beside their mailboxes. The effort has become the largest one-day food drive in the nation.Dave Lundberg, of Indianola, is a spokesman for the National Association of Letter Carriers. He carries mail in Des Moines and says he usually has a sack weighing 35 pounds or so. On this food drive day, he acknowledges those big cans of soup will quickly weigh him down. But he says it’s important to give back to the community.Carriers will collect the donations, rain or shine, and deliver them to participating food pantries and shelters.