Food and water (and medicine) for up to a week is highly advisable. Services will likely be running again by then or at least other supply chains in place within a week, but not within 24 hours. Another thing people do is fill the bathtub if they are not using it and keep that on hand as a source of (usually) non-potable water.
A weeks worth of food and water really isn't practical when moving from hotel to hotel on a trip, unfortunately. I will be trying to strike a balance between being prepared and being mobile; basically, I don't want to be dragging a rolling bag of nothing but food and water between hotels. My hope is that larger hotels might be prepared to provide some water and food for guests, should an emergency arise.