I've always been on the receiving end of these Quality Manuals rather than authoring one. They are really just a list you need the co-packer to conform to. Each bullet point of that list has a description of your expectations. Companies will sometimes use vague descriptions i.e. "have an effective way to monitor your CCP." they don't tell you what they believe or want that CCP to be or whats effective so they (you in this case) can step back and access. It might be a superior approach in hindsight because you will be more able to gauge the level of a co-packers competency on topic XYZ or how serious they take it. I've received Quality Manuals from massive companies that quite literally took an SQF check list and slapped their name at the top. If you are contracting a co-packer you'd want strict controls on things like ingredients keep that in mind which will fall under approved vendors/ingredients.
I have also received Quality Manuals from smaller, but still pretty large imo 50+ co-packers according to them, with a written manual. Still very similar to an SQF set of expectations with controls for ingredients LOT coding etc. I will include the index of what I would use as my template but bear in mind this was only about a 20 page document.
Be very specific on expectations and you might only hear what you want to hear. Be vague and they'll show you how much they know.