Apply coupon code when cart is empty

Question

Would there be any easy way (or any issues) with allowing a customer to enter a coupon code before putting any items in his cart?

Answer 1

The coupon code can be added at any time.

All you need to do is create a coupon code form somewhere using the {cartthrob:add_coupon_form} tags. http://cartthrob.com/docs/tags_detail/add_coupon_form/

Really it's just a matter of creating your site's flow so the customer reaches that form first. It might be that you put the form on the homepage or you could create a separate page for it then do some kind of redirection to that page if the cart is empty (using total_items tag within cart_items_info).