core + pending (Pending Extension): these terms are pending wider review. Feedback is welcomed!

menuAddOn

Defined in the pending.schema.org extension.
Canonical URL: http://schema.org/menuAddOn

Thing > Property > menuAddOn

Additional menu item(s) such as a side dish of salad or side order of fries that can be added to this menu item. Additionally it can be a menu section containing allowed add-on menu items for this menu item.
Values expected to be one of these types
MenuItem
MenuSection
Used on these types
MenuItem

Source

https://github.com/schemaorg/schemaorg/issues/1541

Schema Version 3.3