Be Prepared
My parents had Tom Lehrer records back in the 60s and we listened to them as a family. I was born in 1959, so a lot of the references went over my head. I was about 15 or so when I realized the line “If you’re looking for adventure of a new and different kind and you come across a Girl Scout who is similarly inclined, don’t be nervous, don’t be frightened, don’t be scared. Be prepared.” was a reference to birth control!
Most of the other stuff I figured out from articles in our Encyclopedia Britannica or reading the newspaper.