Give a discount on food purchases so long as people agree to having every purchase tracked abd their data sold to marketing companies so they can figure out how to manipulate people into buying more shit they don't need.
People's food purchases are already scanned in before they buy them, so all that's needed is to get people to scan in some kind of card to connect their purchases to their identity. A small discount can be offered so people will fill out a form connecting their identity to the card and then every time they scan the card with their purchases we can track everything they buy forever.