I've had the traditional book and cd bags for quite a while. Sometimes they circulate, sometimes they don't. It seems mostly based on how visible they are, but their circulation has been steadily dropping over the past few years and I've decided we need to get them out there! Towards that end, I've combined them in packs of four, added an insert about the importance of audiobooks and some additional resources, and tech services cataloged them as toys. In the first week or two of locating them by the toy bags and packing them in larger kits, they circulated immediately, so I think this worked out well.
I have noted in the listing of materials when the book + cd is out of print or if the isbn only indicates the pb. Some sets were purchased from other vendors.