This text is lovely and has many interesting info. Just to note an approach from personal experience that has worked well for several different collective kitchens I have participated, which is not really mentioned here, unless I missed it.
We would go to open-air markets in the morning after they set up and give a small flyer asking for food donations at the end of their shift day. Talking to them was also important, if they felt like doing so, of course. After a period of time, we would just show up just before they were closing and get a lot of food from some specific greengrocers, that were glad to help.
I have to note it was not on a daily basis, it was weekly and not for a mobile thing. Still it was food for a high double digit number of people. And every time before cooking we decided what we would cook, depending on what we had available. Also, all the equipment was donations and anyone could participate in the cooking (actually encouraged to do so since it was not charity, it was collective cooking), and there was a free contribution box for money, through which we would get things like pasta, rice, oil. there was one rule that I liked for the people eating, it was to wash their dish and utensils after their meal. If food or fresh ingredients were left, we had them available for people to take them after eating.