If there was an apocalypse, I assume there would be fewer people alive than there are now.
There is plenty of places to grow things if we all live like homesteaders on 2 or 3 acres of land. Takes about an acre per person to feed someone on today's diet. Less if you're a bit smarter about what you do. A bit more needed if you want to not die if you have a bad season.
Santa Clara County, the heart of Silicon Valley is 1290 sq mi. That's 825600 acres, if every man, woman and child had 5 acres to raise crops and livestock that would support 165,120 people, or about 41280 small families. (I don't think anyone would want to farm more than about 15 acres alone anyways, not without a tractor)
So that means a thriving suburban community of 1,894,605 today would be reduced to no more than 165,120. So an apocalypse where only 1 in 11 people survives is sustainable. Any more and conflict is likely as people fight for resources to avoid starving, that would most likely result in far more deaths and bring the population far below what is needed.
I used silicon valley as an example, as I am familiar with the area and I felt that it has a pretty representative population density. For people on the east coast, places like Long Island would have to be abandoned entirely for a large population to survive. It could support some people, but I doubt anyone could come to an agreement on who could stay and who would have to move further inland. My rough guess is people would have to spread out as far as all of Pennsylvania to handle that 9% of survivors from NY and NJ. That kind of population pressure is likely to create a ripple of conflict in many regions.