No. I guess that would mean a bag belonging to or containing some specific bananas ("bag of the bananas"), not something you'd often have an opportunity to say. I think you meant to say sac de bananes, but that isn't it either. A sac de bananes is a bag containing bananas. What we've got here is a bag that looks like, or metaphorically is, a banana: un sac banane.Sac des bananes?