Plugin for VirtueMart 2 that automatically adds a product on checkout.
Create the zip package and install it like any other Joomla extension.
Open the plugin configuration and set the ID of the product to add (you must create the product in VirtueMart before).
That product will always be added to the cart as soon as the user reach the checkout stage.
If the user removes it, it will not be added again during the same session.