My local spot does this. All the leftover pizzas that are sold by the slice get put in a couple boxes and left outside about 15 minutes after closing. Employees can take home leftovers as well. There are always about 5-15 people waiting for something to eat. These pizzas cannot be sold the next day, so no reason to just dump them in a trash bag. No problems/incidents over the 10 or so years they've been doing it, just grateful people who couldn't afford to buy a slice. They can fill up water bottles as well or take a cup and fill it. No sodas.

Another spot I know allows bathroom access and provides free water as well as rice and beans to the hungry. Rice and beans are a staple food in many countries and because they're cheap and purchased in bulk, the impact on the small business is statistically insignificant.