This would be handy to checkout messed up systems to be able to tell apart easily whats has been touched.
Is there already something that makes this? The easier way it comes to mind is to dpkg --get-selections, debootstrap, chroot and install the selection and then make the diff. although it looks like overkill when you just want to check out a few files maybe just find out where the file came from with apt-file, download the package, extract the file and do the diff any brighter idea? greets! aL