It's yogurt. In one scene, we can clearly see the text "MeierietYoghurt" on the side of the carton. "Meieriet" means "The Dairy" and "Yoghurt" means yogurt. The yogurt is from the fictional dairy "Nordland Meieriet", and the packaging was especially designed for this movie (probably because in Norway, with a few exceptions, yogurt doesn't come in a packaging similar to milk).