Depends where and when, if it's in the UK or USA and it's winter, there would be little chance of surviving more than a week, maybe two for a few amateur survivalists (no bunker). Shops keep less than 3 days supplies, and the distribution centers all need electricity and comms to work. Your oil fired central heating gone as well, you need electricity to work the fuel pump. Hope you have a solid fuel stove and coal/coke/wood to burn in it.
Rural Thailand you could probably survive forever, as they're not that reliant on the modern world.
Look in your kitchen, and guess how long you could last on what you have outside the fridge and freezer? and your taps won't work without electricity. Don't you wish you had spent 700bht on a big sack of rice and 300bht on a ceramic water straw?