Hi Aaron! Can you share more details with us about this feature request? We’d love to hear more!
it would be nice to be able to choose an additional paid option such as a guarantee, insurance or another product which is linked to our offer. for example if you buy a sweater at 20 € then you can click just below to add in one click the ebook at 5 € in the payment basket.
for the events it can be a place + a meal or drink or sweeping paid option.
for the Booking it can be a cancellation insurance for example or an additional kit of sports equipment at 10 € in the price of the session. in any case it is optional, we can give it the name we want (possibly a picture) and a price. the upsell must intervene just before paying, after having filled in all the other information. 
I wish they hurry up and come out with this feature! Huge game changer