In the Web Store and Inquiry Catalog modes, the cart of a logged-in customer is saved when the checkout form is submitted. The customer can restore this previous cart the next time they log in. Customers can have accounts when customer accounts are enabled.
When the current cart is empty and a previous cart is available for the logged-in user, the cart button is replaced with the Restore Previous Cart button.
Also the empty cart will contain the cart restore button:
After the button is clicked customer previously purchased products will appear in the cart.
Please note that the button is available only for logged-in users with a previous order.