Leftover bits in the transmisison gasket set

I'm putting my 4-speed transmission back together, I have a 4-speed transmission gasket set from Vick's and there are a few bits and pieces that I'm not sure about.

Picture here

There's the big O-ring, about three inches in diameter, looks like something to do with the differential (which I haven't taken apart - was working fine before and looked good when I opened the case). What's it for?

There are four smaller o-rings. One is for the reverse shaft and one is for the pivot for the clutch release lever. But what about the other two?

And finally, what's that cardboard gasket for? All the other gaskets in the set I've found a home for.