When generating a pack, any contract in the pack (and the pack itself) will draw information from the three sources above - the Requisition/Approval-to-Hire form, the Onboarding Data, and the Candidate (application) Data.
What is to be noted here is that data entered into the Contract will not be passed onto the Email Automations. If you have issues with some of your fields in the email automations turning up blank, it may be because this field wasn't completed in an earlier form.