One-Scene Wonder: Lots of people quickly come and go, but Patrick Troughton stands out in his one-scene turn as a doomed river-barge operator named John Millen in "Parasites".
Since the plague played out over time the nuclear subs would have been able to monitor the progress of the plague through public broadcasts and dispatches from their command authority. Doubtless the same would have happened with the SSBN fleets of the United States, Russia and any other navy operating such submarines.
Rescued from the Scrappy Heap: Sarah spends a majority of the first season being useless at best and outright villainous at worst. But during the second season, she begins to put more effort into acting like a better member of the group.