savehist-additional-variables

savehist-additional-variables is a variable defined in `savehist.el'.
Its value is

nil

Documentation:
List of additional variables to save.
Each element is a symbol whose value will be persisted across Emacs
sessions that use Savehist. The contents of variables should be
printable with the Lisp printer. You don't need to add minibuffer
history variables to this list, all minibuffer histories will be
saved automatically as long as `savehist-save-minibuffer-history' is
non-nil.

User options should be saved with the Customize interface. This
list is useful for saving automatically updated variables that are not
minibuffer histories, such as `compile-command' or `kill-ring'.

You can customize this variable.