Currently, MassageBook does not provide an inventory management system. You have the ability to record individual Product sales, but there isn't a way to list them in a menu. You would need to enter the product name each time you select that option in Cash Register. Depending on your browser, it might offer suggestions as it recognizes regular entries.
While we're not actively working on this feature right now, be sure to keep up with our bi-weekly Release Notes so you'll be the first to know when updates are made to this feature!