When Baldur's Gate 2 was first released, the Collector's Edition of the game came with a Bonus Disc that I think had some extra in-game items and other stuff on it.

Does the GOG version include the content from that disc?

I have both the GOG version and the original CE. I'm wondering if I want to somehow get the stuff from my Collector's Edition Bonus Disc into the GOG version or if that's unnecessary.

EDIT: Oh yeah, there was ALSO a pre-order bonus disc if you got it from certain retailers (Gamestop? I forget...). So there were actually TWO bonus discs. Is the content from both in the GOG version?

Not sure about the pre-order bonus material, but I'm pretty sure the two merchants and extra items from the bonus discs are in the GOG version. Can't say with 100% certainty though, as I modified my game with the BGT mod and I don't recall if those things are added with that mod or not. But they were in my modded game when I played through before Christmas.

The latest official ToB patch contains the bonus merchants. Since GoG versions are fully patched, they should be there too.