For working with Debian packages, one method of maintaining them is to put them in git and use git-buildpackage to build them right out of the git repository. There are a few pitfalls with it, notably around if you forget to import the upstream you get this strange treeish related error which still throws me at first when I see it.
Part of maintaining packages is to be able to fix security bugs in older versions of them that are found in stable and even sometimes old stable (jessie and wheezy respectively at the time of writing). At first I used to do this outside git because to me there wasn’t a clear way of doing it within it. This is not too satisfactory because it means you lose the benefits of using git in the first place, and for distributions you are more likely to need collaboration with, such as working with the security team or help with backporting.