Both Kate's and Nanren's answers are good. I just thought I'd add, for context, although you may already know it, that 1) Volkswagen cars and buses were extremely popular among young people in 1960's America, and 2) mind-altering drugs were extremely popular among young people in 1960's America. Americans would automatically know that the line refers to drug use, because drugs are one of the first things we all think of when we picture what the '60s were like.