Well, I guess it depends on the particular Bulgarian. If I were you, I'd go for stuff that's not on the news. Maybe some traditions around celebrating Fourth of July apart from fireworks and red-white-and-blue stuff. What do you like (or dislike) about how it's celebrated. How are different minorities and foreigners celebrating it, if at all? Or a brief note in the beginning on what lead to the American Revolution. The significance of the Declaration of Independence. Whatever comes to your mind about that holiday.  And here's one I'd ask - how did the US get from the founding fathers saying things like "I have sworn upon the altar of god eternal hostility against every form of tyranny over the mind of man." and "Religious bondage shackles and debilitates the mind and unfits it for every noble enterprise...." to actually debating whether evolution should not be taught at schools? 
As for Bulgarian economy and politics, I think you can just say that you don't follow these. I don't. They're boring. And debates in particular are pointless, annoying, "he did it" accusations that only waste your time. They could ask you about the clandestine repainting of the Soviet Army monument (and its equally clandestine cleaning). Apart from that I have no idea.
And as a complete off-topic note: You know how you sometimes have these "Really, Sofia?" moments? I just had a "Really, America?" one :P http://www.youtube.com/watch?v=r0gsaDxK884