aww, here I was hoping for a steam only release.
The disks mean nothing! They become out of date the day of release.
As far collectors stuff you could just use the extra 10 dollars you'd pay to buy in game vanity stuff, and I'd imagine T-shirts will be for sale somewhere hopefully. I can't think of anything and the things already listed sound boring.
Actually now that you mention it I don't think there should be a collectors edition. I don't see the point. I'd much prefer a digital download for an MMO with nothing else. Just purchase a key from Planetside2.com or steam and download it. Simple and easy.