Just go to the plug-in that you want to save and go to save settings...
This might be a little easier than importing session data... Maybe not.. But this is how I do it.
Make sure your also go to settings preferences and set the "Save plug-in settings" to the root folder so it is available from your other session.
I am also assuming that you tracked three sessions already and mixed one, and are going back to mix the other two. If you tracked and mixed one, and are going to track more, I would use import session data (option + shift + I) so that all the tracks are already there and named, with all plug-ins, routing, etc... Heck, if its the same band your inputs should all be the same too...