when we build an os snap using live-build (our standard method), then live-build produces a .manifest file that contains the list of packages (and their versions) used to assemble the rootfs. with cdimage builds we published these so people could verify what is contained in their install. snapcraft should have an option to release this file along with the .snap as well. http://cdimage.ubuntu.com/ubuntu-core/vivid/daily-preinstalled/current/vivid-preinstalled-core-amd64.manifest is an example of such a file