I think that describes a lot of potential extras for this.
My number one addition would be Reach, but that would be a feature, not an extra. (If it was an extra, that would be messed up.)
I think my vote goes to Conversations From the Universe with more conversations, the Bestiarium from Halo 3, maybe expanded and updated but with mostly the same content, the "making of" content, maybe toss Forward Unto Dawn in there (a disk or a code to download it, none of this streaming nonsense I've heard about and no requirement to have XBL gold or be on-line), and a Grunt plushie. Come on. Come ooooooooooon. You know you want to. You know it's wanted. I have one but so many people missed out because they didn't know or they were short on money for a while or the shipping was ridiculous, and I would be fine with having two. Gripyap could use a friend. Come-ooooooon.
It's all unsignified sound and fury, though, I won't be able to afford to spend more to get it on top of the console. Maybe if they'd waited and not stuck to this dumb anniversary timetable or not made it exclusive to a relatively new console....