At some points, I have WISHED that this would happen, my life is a lot stable, I don't like, I like adventure. What I would do is find whatever I could use to help me survive in the office and get back to my car (scissors, some food, whatever). Then, see if I can find someone I know and trust. Call them on the phone or I can, pass by their house. If I can find someone, I will take them with me. If not, I am on my own. I go to the local gun shop, and get a gun and ammo.
If I have too, I will buy them, if I don;t see anyone inside, break in and take as much as I can, literally stuff my car with guns and ammo. Also, knives, swords, bows and arrows. Also binoculars. Guns are cool, but not really useful in my opinion if something like this happens. Too much noise. Then, do a raid in the city and get food (milk that last a long time, canned stuff etc) so I have something to eat. Then, off the woods or the top of building with no other buildings close to it (do someone can't jump to my roof from the roof next to me.
Also, since I going to be on a building, water is not an issue, since roofs have drinkable water (at least where I live). And it's on bitch, I am going to stay there and watch and still try to communicate with someone I trust. I would not take ANYONE I don't know well with me. Not even a priest.