Looks great, but did you scale it a bit big? From what I've seen from ODST gameplay, it's a litle bit smaller, but it could be the mannequin.
Also, I've had this idea for Spartan armor as well, but how about you put an actual backpack inside of that backpack and make it a functioning backpack! Make the details of the armor backpack match that of the opening of the real backpack. So at Cons you could carry all your swag and what not in it. Just a thought, but I think it's a great idea.