I honestly think its crazy that gems like these haven't had an official release (yet):
Big Sur (4/4)
Carry Me Home (Yeah, I know they vetoed it being on MIC)
Hard Times
California Slide (I'm Going Your Way)
Awake (Demo)
Please Let Me Wonder (Mike Lead)
Little Red Book (Demo)
Walkin' (Demo)
It's A New Day
Add Some Music (Alternate Lyrics)
Tears In The Morning (Alternate Version)
My Solution (I would argue that there's enough novelty value for a release)
Won't You Tell Me (Demo)
Out In The Country (Both versions, honestly)
Sweet & Bitter
Daddy Dear/Susie Cincinatti (Demo)
Rollin' Up To Heaven (Maybe a bit X-rated, but its sure a fun listen!)
Short Skirts (Catchy instrumental)
Sea Cruise
Marilyn Rovell
You've Lost That Lovin' Feeling
That Special Feeling (Demo)
Calender Girl
Please Darling (I'm Begging You Please)
Drip Drop (Teardrops On My Bed)
River Deep, Mountain High
Stevie
Oh Lord
I Feel So Fine
Water Builds Up
Don't Let Her Know She's An Angel
Do You Have Any Regrets
Brian (Thank You)
Chain Reaction of Love
This Could Be The Night
It's Not Easy Bein' Me
You could also collate all the available outtakes (released or otherwise) and create Deluxe Editions of every album. For example, you could make a Deluxe Version of Love You with the following tracks added:
15. It's Over Now (Demo)
16. It's Over Now (Love You Audition)
17. They're Marching Along (Little Children) (Love You Audition)
18. Still I Dream Of It (Love You Audition)
19. Love Is A Woman (Love You Audition)
20. Mona (Love You Audition)
21. Airplane (Love You Audition)
22. Let's Put Our Hearts Together (Love You Audition)
23. I'll Bet He's Nice (Love You Audition)
24. I'm Bugged At My Old Man (TV Rehearsal)
25. I'm Bugged At My Old Man (TV Special Version)
With Disc Two being the Adult/Child album of course.