I can think of plenty of companies I'm nominally a customer of, but which were actually chosen for me. My mortgage and student loan servicers, for starters, since my loans were sold and I had no choice about who bought them.
Conceivably you could do some kind of guerrilla farming or something... as long as you steal all the supplies and use land no one would noticed months worth of cultivation on.
Otherwise, no, you would eventually have to exchange money with someone in order to feed yourself on a regular basis.
Well, there's also charity. If you subsist exclusively through soup kitchens, technically you're not buying things... but things are still being bought on your behalf.
And like, are you learning all your farming by trial-and-error? You'll probably starve to death first. Might be worth paying someone for some education.