I just saw the Red Box ‘Desolation of Smaug’ and was underwhelmed. I don’t recall a romance between Killi and Evangeline Lilly’s character (or her character for that matter), the wooden tubs were sealed/the ridiculous fight with the Orcs never happened, where did Legolas come from?, Smaug v. Bilbo was disappointing, yecchhh .....
I would agree that having the barrels sealed would have ultimately made it a better scene. Have them float by the orcs, with the orcs arguing about whether to check them or not.
Legolas was the son of the King of the Elven Kingdom where the dwarves were imprisoned.
It's entirely reasonable he'd be around, even though not mentioned in The Hobbit.