Going into The Desolation of Smaug, I thought for sure that the Legolas/Tauriel bits were going to get the axe in my imaginary one movie edit. But I actually liked Tauriel, they actually invented some good material for her. Her speech about starlight was actually rather enchanting, so that at least should stay in. It goes a long way towards painting the elves as more sympathetic.
Most of the Smaug bits after Bilbo's dialogue with him should get the axe though, that gave me Episode 2 flashbacks. It should be pretty easy to do, after all nothing happens to advance character or plot in that section.