Well, if you're trying to fill up a BD-25, those are pretty good audio options, pretty complete. I seem to vaguely remember someone on this forum claiming either that they or someone they knew had a DTS audio sound disc (or something like that) that was used during the 1997SE Theatrical Reissue and were trying to transfer it to DVD. It was before I became a member and was just browsing; even then, I think it was an ancient thread. Did anything ever come out of this? If so, it could be a good audio track.
As for special features, maybe you would consider putting both the laserdisc and VHS Special Edition documentaries. Each movie could have its VHS documentary and the laserdisc one can possibly be on either the ANH disc or the ROTJ one. The VHS would be a good inclusion since many people had the VHS, so are used to that documentary; additionally, the VHS version is split into the three movies, so all three discs can have a little SE feature. Of course, you may also want to preserve the LD version since it's better quality and different. Another special feature would be the trailers, as previously suggested.