The receipts for food aren’t so that you can return it. They are for expenses record keeping. For example, some jobs have a food allowance; or special tax concessions for food bought while working. But to get those benefits you need to have evidence that you bought the food.
Just mention lemmy from time to time on other platforms; not to say “please come here”, but rather just to let people know that lemmy exists and has interesting stuff on it. People will check it out if they are interested.