Look you’re going for: Clean and comfortable, but not couch-surfing wear
The traditional dinner-and-a-movie is the quintessential first date because you get to learn a lot about that person during dinner, from their current situation to their eating style. Then the movie gives you time to recap everything that just took place and assess the situation. But don't worry, she's doing the exact same thing, and one of those things she's assessing is how you decided to dress. Give her Ryan Gosling in The Notebook, not Blue Valentine. A casual button-down shirt, comfy chinos, and a medium-weight bomber or baseball jacket in preparation of the inevitable cold shiver she'll experience in the theater will let her know that you've carefully plotted out the evening just as much as the wife in Gone Girl. How you react to all the deception in that damn movie will also be on her mind, so tread lightly, my friend.