Wix Bookings feature to create a list of add-on or a la carte services the client can add at Booking Checkout such as enrollment fee, materials or textbook fee, lunch/meal, private class, etc. Add-ons can be make active or inactive to appear at Booking Checkout for Services and Pricing Plans. Add-ons can be required for certain booking services or pricing plans (one-time or recurring) such as a program/class enrollment fee for all clients. #featurerequest #wixbookings #bookings
Once again, thank you for your detailed feedback! 
YES! I 2nd this request.
@Amanda_Goodfellow Thank you for your post! I recommend that we start a new post in the Feedback: Wishlist area (since the original post is very old) and I don’t want your request to get lost. In the meantime, I’m going to close this topic to help others in the future.