These are per-booking options that can have a quantity and a price.
When booking, a list of optional extras appears at step 2.
When you edit a booking on the Manage Bookings page, you can edit the options directly: look for the expandable section below the guest list.
Create and manage Optional Extras via admin menu → tariffs → Optional Extras
Each optional extra has an access level, so an option will be hidden if the logged in user has insufficient access.
You can set a date range through which an option operates, it won’t be shown unless the booking overlaps this date range. These date ranges are optional (leave blank if not needed) and don’t need to match season dates.
You can change the title of all the Optional Extras from Optional Extra by creating or editing config item OPTIONAL_EXTRA_TITLE. This config item should have Role_Read set to PUBLIC.