This gist contains hack-y python scripts that pull registration content (as JSON) and any files and wiki pages into a directory structure. One then runs a bagit script and mixes in metadata to get a BagPack.
NOTE: the bagit script I used wasn't BagPack-aware, so it didn't actually include the files under ./metadata/ in the manifests. Also all the bagit metadata is just defaults; these examples are just to show the "shape" of the results.
Check how example items show up on archive.org in this collection: https://archive.org/details/cos-dev-sandbox
Description HTML is probably going to link to any child registrations (items). Should also link back to, at least, collection page.