Develop Memorandums of understanding in each city with local mobile food vendors (aka roach coach) that usually work at consturction sights.  They have the vehicle and a grill for cooking.  They could be called to the scene of long term incidents to supply food for teams like fire/police and rescue or could be sent to evacuation stations to feed people coming in.  This idea can be applied to major sports arenas too, since they already have the cooking equipment.  The city can provide the food from local vendors using the same memorandums of understanding.  The cost is very low until the service is needed, but would allow for several mobile kitchen to be placed at critical areas within hours of an incident.