Weirdly, I just had to teach a crash course in First Amendment principles to a bunch of high schoolers.
The issue that sparked the most discussion was "state action," - in other words, what is necessary to trigger the First Amendment.
(Well, that was the second most-discussed part. The first most discussed part was when I introduced the text ..."Congress shall make no law ... abridging the freedom of speech ..." and had to explain that it was all a lie. By "Congress" it doesn't mean "Congress" and by "no law" it doesn't mean "no law" and by "speech" it doesn't mean "speech" ... which was kind of funny for the literal-minded.)
As an aside, re: questions regarding laws re: GMO disclosures and the like ... I suppose it depends on how you define censorship, but yes, compelled speech is also a FA concern; it's just that the standards for compelled speech in commercial contexts is different.