Nearly every day, five delivery vans from Second Servings of Houston navigate the streets and highways of America’s fourth-largest city, picking up leftover foods from more than 400 restaurants, supermarkets, and manufacturers. Crisscrossing the city with an average of about six tons of material overall, the vans deliver the foodstuffs straightaway to charity pantries, soup kitchens, homeless shelters, community centers, and low-income housing complexes, where the potential waste becomes meals f…