In short, by the community. The community fridge near me is refilled mostly by:

People who have to buy more than they want (ie pack of four items, but only need two).

People who made to much food/leftovers, or who just want to cook for others

Weekly community cooking event.

Overproduction from community gardens.

Spillage from restaurants.

Spillage from the grocery store.

People who want to cool their stuff

You can’t ask this, that’s very anti-communist of you

You see I will be a professional shit poster for the regime, they will allow that and I won’t be forced to work the camps