And yet shoplifting law generally states that if the customer purposely hides an unpaid-for item from view (though common sense would suggest this probably doesn’t mean burying it under other merchandise in a cart) this constitutes shoplifting. So the person is not free to do whatever he or she wants with it, yet.
No but peacefully adding an item to a shopping cart is legal possession under the presumption one will either pay for it or return it to the shelves.