Two things:
① Copies of all declarations involved in this shipment (both those signed by suppliers and those you signed)
② A diff view—which item number → uses which packaging → corresponds to which declaration
The second item is most often overlooked. When a buyer receives a stack of PDFs with no index, they have to ask you again anyway—effectively wasting effort.
Recommended diff view columns: Supplier | Box Type | Item Numbers Covered | DoC Number | Signature Date | Signed By | Next Review Date