Try to come up with some set examples (ie: 5or 6) that can be applied to a broad range of topics. A really good one to use is the civil rights movement, it can apply to a bunch of different topics (media, politics, etc).
I wouldn't bother with quotes, I'd focus more on improving your writing/coming up with set examples. It won't hurt though, but if you fudge up the quote and the examiner notices, it can only detract from the essay. Plus it's added stress to remember it during the writing sample
That being said, I was blindsided with a prompt about law that I couldn't apply any of my examples to. My first essay I killed though, yay for World War II and the Mars rover (don't ask)