Q134: What are additional products?

Additional products are either extra charges always added to the bill (such as visitor's taxes or final cleaning) or one-time optional products or services (such as airport pick-up, water skis for motorboat rentals, etc.), or recurring products (such as breakfast). You can specify the products, pricing and other options in the settings tab. It's up to you to decide whether the products are selected by default and whether only the administrators can add/remove them to reservations. If you allow users to book additional products, you can also specify till when they can add or remove them. By default the users can pick additional products only at the time of reservation.

See also this FAQ question.