Journeycake is a type of simple cornmeal flatbread. It was a staple food in early America.
According to the cast, the actors playing Jemmy would want to go home or do other things after just one take. They would say things like "I'm doing one more acting and I'm done." Jemmy's line "I woke up! Now I'm done?" after the MacKenzies attempt to go through the stones is an example of this antic.
Claire tells Jamie that sperm can live in a woman's body for up to a week. Actually, it's up to 5 days.