We have a similar system in many parts of pune with small roadside eateries selling vada pav, dosa, misla etc. Some pay for extra portions and is given to others who can't pay.
During the pandarpur yatra too, some restaurents give free food, some pay for extra in their bill for feeding the varkari yatris. In addition to feeding pointss set by corporates, companies, trade groups and charities.
It is a good practice, hope it spreads of other cities too to ensure that food we take reaches others who can't afford, and supplements their subsistence level food.