Yes. Guests can purchase multiple gifts. When you find an item you would like to purchase and click the BUY NOW button, the next page will redirect you to the store from which the item was added to "Add To Cart".

Once you have added the first item, simply return to the registry and do the same steps: Buy Now, Buy This Gift At The Selected Store, and then you can add the next item to the cart on the store's website. After adding the last item, you will notice that the others are still in the cart and ready for checkout.