Almost nothing is self sustaining. You are only as self sustaining as the drive to your nearest supermarket. And all of those stop working the instant the switch turns off. Sure, you might get a month or two of bonus time if you raid the place for all the non-perishables you can cart off before everyone else realizes the apocalypse has set in, but unless you are able to magically conjure food and water out of thin air, or live in good hunting / fishing country, you are only prolonging your fate. Very, VERY, VERY few people are capable of actually living off the land, and after 4 or 5 months, that's pretty much what you would be doing in the event of a total collapse.
Also, don't forget. If you are even the tiniest bit self sufficient, then the least of your worries will be food or water. It will be all the other people out there trying to survive. And if humanity has proven anything, it is that we can get REAL ugly when survival is at stake.