I know preparation charges are not necessary... anything else that can be
A bargaining item?

Pretty much everything is negotiable, even "non-negotiable" factory warranties. What's worked for me is that I say yes to everything. No negotiating---until it's time to close the deal. Then I delete all the extras. The salespeople have already spend the commission (in their heads) and will do anything to save the deal.

BUT, you have to be willing to get up and walk out. Last car I bought, I walked out of the dealership 3 times. The salesman chased me each time, and each time he dropped his price.