An update on my thoughts here. I looked at the cover again and reconsidered something. All of that must be Gryffindor's. There is a helmet like I said, but there is also a shield with rubies in it. Every stone there is a ruby. It would only make sense that with a sword, helmet, and shield that all obviously belonged to Gryffindor, that the other piece of the armor is his too. Perhaps the "snake-like thing" is an old variation on a Griffin.
So, the question we have now is where are they? Could they be at a vault at Gringotts (sp?) that either belonged to Gryffindor or is now storing his things? Somewhere else? Could one of these things be a horcrux and that is why they are there?