In the city I live (Fortaleza), the cart folds into a small size and fits into a backpack. It takes about 20 seconds to do.
They then put the folded cart into the backpack and put the backpack on their back.
So, in a sense, they are carrying the carts on their backs but it's not a struggle at all...LOL!
On a side note, I had to knock on doors in the projects in Brooklyn when I was dating my ex-wife. One could argue that's just as dangerous as those gators.