It depends on where you are and the quality of life you’re after. There are some areas where squatters have a right to live in an unoccupied buildings, so there’s the shelter. You can dive in dumpsters for many of life’s necessities. Here is an interesting article I read that features a woman who went from rags to relative riches by living with little money. But she still does use some money.
You cannot “live off the land” with 0 dollars in the United States. I just wrote about this in another response, so I’m going to be lazy and paste that answer here:
There is no foot of space where you would be allowed to just be. You would have to purchase the land and pay taxes of all kinds in order to so much as sleep on the naked ground, let alone build a home there. You would have to make some sort of income to pay these taxes, and the government won’t accept tomatoes from your garden. So you’d have to get a job. And there begins the cycle of impossibility. You can’t dedicate all your time to joining the workforce and have any time left over to tend to living off the land.
You may be able to get away with not paying taxes, fees, and for permits for a little while, or even forever, but technically and legally speaking, you’re not allowed to do it.
However, if you’re simply speaking of being homeless, there are dozens of charities and programs that you could take advantage of to sustain life. Food drives, shelters, soup kitchens, clothing drives, etc. But you see, that stuff was provided by someone’s money. These programs, especially with shelters, aren’t meant to be used long term. You can’t just free-load. You have only so long to stay there before they need to make room for new residents.