I have spent some time in NYC, Chicago, Minneapolis, Cleveland, Columbus OH, KC, etc. One thing I noticed is that leaving major metro areas quickly can be difficult especially if you are in the heart of these cities. NYC seems like worst out of all that I visited to get out quick. So that means you are going to be living not off the land but in the city. A city where the homeless are numerous, criminals are numerous, etc. I am thinking a low profile daypack will blend in a lot better (zippers and all) instead of a military ruck. What you need are items to make you comfortable and safe. Good shoes, a warm light jacket, cash, med kit, quick energy food and some basic protection items like gloves, dust mask, eye pro. More then likely you will be heading to a shelter or group area that the city has determined. You will be on foot so you need to move easily and without notice.
Just some random thoughts