In Palo Alto, you have the option to show up to three upsell buttons when the cart is empty.
To set this up you need to first create a new navigation menu. Start by heading over to your Online Store > Navigation and clicking on 'Add menu':
You can give it any name you want, we will call ours 'Cart menu':
Lastly, you need to open up the Theme Editor and click on Theme Settings > Cart:
Under Empty cart click on 'Select menu' and choose the menu you just created: