If you could have played on any album by anyone, which ones would it be?
Obviously any Beatles or solo Beatle album
Otherwise
Bass on Derek and the Dominos Layla
Bass on Elton's Blue Moves album (I'd never dare to play on an album when Dee Murray was in the band)
Guitar on Dylan's Highway 51
Guitar on Traveling Wilburys' first album.
So many more, many quite obscure.