Today, I have a short tip to all people who write Elisp and want to preserve some variable other than user customizations between Emacs sessions. (For user settings, configuring them manually in init.el is the standard way to go.) A classic example would be histories of the user’s entries.
In fact, I already mentioned the persist package a long time ago. It is a fairly small but extremely useful tool. What it does is, well, persist a variable across Emacs sessions. As I said above, I find it especially useful for variables keeping various completion histories. If you write any Emacs tool which could benefit from being able to remember things even after quitting Emacs and starting it again, persist is definitely your friend!