Requirements for packaging

For the last 5 years a Letter of Guarantee has been sufficient for my packaging supplier. However, this year the auditor wants more. Im looking for suggestions on evidence I can provide to support the food safety controls of my packaging suppliers. Both of them are just printers, so they may use different suppliers for the bags they get. Should I be going to each of their suppliers and asking for audits or doing some type of testing on the bags once they are here. They are paper bags for flour. One has a poly liner, the other does not. Any suggestions are welcome. Thank you all. 

We call for the following from our food contact packaging manufacturers:

-LoG or CoC (prove to me the bags/containers are food grade compliant)

-Emergency Contact List

-Specs for all products sold to us

-Current GFSI audit and cert

-COI

-Lot Code policy/explanation

-Additional forms based on our customer requirements (but not relevant to SQF)

And it sounds silly, but ask them about their allergen program.  I worked for a company that used pink colored poly bags, and the pink colorant was derived from shellfish shells.  That example probably doesn't apply to you specifically OP, but in general it's a good thing to ask about to help prove you're not likely to get a shipment with a stray Snickers wrapper tucked inside.

Ask for food grade certificate, COA & migration certificate. If it conform the regulations then go ahead.