By tracking what food has been purchased, and on what date, the user can be alerted to anything potentially going to go to waste and take action. The action can be to eat, adjust their future purchases, or in the meantime bring the near spoiled food to an agency for the redistribution to others. Using bar-coded supermarket receipts could streamline the data collection while creating opportunities for collaboration and sustainability.
http://sicamp.org/si-camp-uk/scotland-2011/ideas/numnums/