Here in the UK I have planned for just such an emergency.

In an urban area I feel that it is unwise to count on any type of hunting, foraging, gathering or purchasing.
There will be a lot of competion for any available rescources.

I keep bottled water for a few days, and have a water butt filled from the roof for the long term. I doubt that such water is safe to drink as is, but have a large supply of chlorine tablets to treat it.

I keep basic foods for about 3 months, mainly tins.

I have a small wind turbine and some PV modules, this would allow lighting and refrigeration to be used indefinatly, and would allow very limited use of other appliances.

I have a kerosene cook stove, lamps and space heater in addition, and loads of candles.

For any long term sheltering in place, dont forget plenty of good warm all wool blankets.
Although a good sleeping bag is useful if you have to evacuate, blankets on a proper bed are more comfortable for long term use.
If electricity is available, but most be used frugally, an electric blanket uses much less than heating a house!

Likewise keep a stock of very low power light bulbs, both to save money if times are hard, and to use from a generator, battery, or other limited power source.