Checkboxes on signup form confusion

I have a question in regards to how to do this, I am running amember 3.0.2PRO here is what I’d like to do:

Level 1 Membership ($XX)
Level 2 Membership ($XX)
Level 3 Membership ($XX)


[ ] Extra Feature 1 ($X)
[ ] Extra Feature 2 ($X)


So the user can select any level membership, but in addition to their membership on the signup page they have an option to add both, one or neither of the additional options.

I am using clickbank for my payment processing, so I am curious how exactly I do this in amember so that if the user does a Level 1 Membership with Extra Feature 1 they not only get directed to the correct price/product within amember but they also get forwarded to the proper price/product at clickbank for payment.

I’m pretty sure that this is pretty easy to use but I haven’t quite figured out in regards to the custom fields and all.

Thanks!