When a file is added to a shopping cart we store that file in the database. If the customer puts that item in save for later, or leaves the cart, you will see those folders in your File Manager with the Order ID that was assigned to that session. If you look at your Open Carts or Saved For Later items, you will notice the Order ID listed which will correspond to the folder numbers in the File Manager.
Below shows an Open Cart Order ID.
The same Order ID is listed in the File Manager for the file that was added in the Open Cart for the customer.