There are probably a billion people in this world who have never seen an electrical grid, and they manage.
For the rest of us, survival really comes down to population density in your area. It's a simple matter of supply and demand... competition for existing resources. In certain areas, having a generator and stocks of food is a great way to paint a giant bullseye on your back.
I would imagine less populated agricultural areas would pull together as communities and survive, but the cities and packed suburbs wouldn't fare so well. You would need roughly an acre per person to survive long term.
I run what I call a "living seed bank," which is a small garden with a dozen or so heirloom veggies. The garden provides some food for the table now, but provides me with enough seeds that I could expand the garden to meet my needs. In extremes, I would plant enough for my family, then distribute the extra seeds to my neighbors so they wouldn't come over and eat me. (I'm probably quite tasty)
I do have guns and ammo stashed, but that's a last resort I would rather not have to employ. (unless we are invaded by zombies
) I would love to feed everyone, but obviously can't. I am mentally prepared to defend what's mine if it comes down to that. Let's hope it never does.
Water isn't really an issue. There are several springs in the area, and I could easily make dew traps if I had to.
Shelter isn't much of an issue either. If it comes down to it, we would live in one room and heat that room as little as possible. Probably wear a lot of clothes and sleep in sleeping bags.
I have a small solar recharger that will charge up my laptop, and also have a 1 TB "Passport" drive with many thousands of ebooks. If the grid fails and the net goes down, I have enough information to make it. My library contains a nice collection of medical texts, engineering texts, alternative energy texts, textbooks on mathematics and the basic sciences, books on all types of gardening and food storage methods, herbal and traditional remedies, and just about anything else you can imagine, plus tens of thousands of the greatest novels, works of philosophy, religious texts, and so on.
So how long could I survive? As long as it takes.