Now those are really cool, but they don't scale up for supplying a major city in rubbles with water and food...

I think shipping is the only way to realistically move the quantities needed for supplying million-size cities when there's no working infrastructure. Most really big cities are at or close to the coast. You still have the problem of distributing withing a city without any working roads, but at least you've got shiploads and shiploads of supplies in the harbour.

Shiploads full of useful supplies along with skilled relief workers, trucks to deliver supplies and heavy machinery to clear the docks and the roads so stuff can get unloaded and the trucks can go anywhere ...... That kind of organization isn't something you just improvise. Just think about the recent big EQ in Haiti and how long it took before heavy-duty relief effort was being shipped in substantial quantities. Pre-planning can cut the response time considerably.