If, like me, you’re staying on the peninsula part of Kefalonia and can’t be bothered driving an hour to the other side of the island to hit up the more higher profile beaches mentioned above, Lagadokia Beach is a solid option.
In Kefalonia
Fiskardo (Fiscardo) is one of the few old fishing villages of Kefalonia that wasn’t devastated by the 1953 earthquake, which has resulted in it being the most popular village in Kefalonia (aka it’s v. touristy).
I took the ferry over to Argostoli a couple of times during my week in Kefalonia and can assuredly say that you don’t want to visit the island capital during the afternoon.
If you want to hire a car in Kefalonia (or anywhere in Europe, for that matter), I HIGHLY recommend you learn how to drive a manual car beforehand so that you don’t have to rent an automatic.