At first, I see the progression of textures as the panels fall to concrete and, ultimately, dirt. Even without the milk carton, that's an interesting and strong image.
Then, I see the milk. The inclusion of the carton adds a new dimension, a dissonance, an element completely out of place as you describe in your opening post. It injects a sense of humanity. Who tossed it away? Why was it left there? Why isn't it finished? What drama occurred here?
Then, I see a pattern. An exclamation point made from the vertical alignment of the synthetic elements (upper panel, lower panel, concrete) and the dot embodied by the milk carton. It's punctuation!
Well, this is a cool photo. I obviously like it a lot.