At minimum: a valid food safety certificate with the right scope, a signed product specification, an allergen and origin statement, a description of the traceability system, a recent certificate of analysis, proof of insurance, and the commercial terms including the Incoterm. Everything else is category-specific.
Why it works this way
A supplier approval pack exists so that the decision to buy is documented and repeatable, and so that an auditor can see the basis on which the supplier was accepted. The pack is not paperwork for its own sake; each item answers a question that becomes expensive at the wrong moment.
The certificate answers whether an accredited third party has looked at the site. The specification answers what you agreed to buy. The allergen and origin statements answer what you must declare downstream. The traceability description answers how fast you could isolate a lot in a withdrawal.
What follows in practice
Set an expiry on every dated document and review the pack on a schedule rather than when something goes wrong. Certificates lapse, scopes change, and a pack assembled two years ago may no longer describe the site you are buying from.
Ask for the documents before the first order rather than after it, because a supplier who cannot produce a specification in a week will not produce a deviation report in a day. The supplier approval pack sets out the full list, the sequence and what each document should actually contain.