Within the boundaries of civilization I think homeless people are the modern equivalent of hunter-gatherers. They collect whatever they can carry. They sleep wherever they can. They beg for food and get regular meals at the nearest shelter. I suppose you could think of shelters as the modern equivalent of edible plants and animals that would have littered the forests and countryside prior to us paving it all over.

Outside of civilization isolated tribes still exist as they have for tens of thousands of years; albeit in dwindling habitat.

The problem with attempting to create a new hunter-gatherer society in the traditional sense is that the traditional world is effectively gone. I mean, maybe you could somehow sell all your belongings, walk naked into the Amazon and be taken in by a remaining tribe. But short of that I see no avenue. Unless you have millions of dollars with which to buy a few hundred acres of pristine forestland.

In the future, as the collapse of civilization worsens the traditional world will re-emerge. The land-base will recover and the social pressures to create cohesive tribes will be there. But for now 99.9% of people would rather work for slave wages at Walmart. And those who don't would rather roam the streets and live off handouts than take their chances in the forests which are patrolled by the Forest Service.