These sorts of things are better posted before they happen, but better late than never, I suppose. The following list involves the interplay between unaccompanied chant (except for Credo III, which I accompany for non-musical reasons) and solo organ playing. This is what we did this afternoon at St. Peter's Church in Merchantville, NJ. All Propers are from the Graduale Romanum.
Processional: organ improvisation on Nos autem
Asperges Me
Introit: Nos autem gloriari
Kyrie et Gloria: Mass XI
Gradual: Christus factus est
Alleluia Dulce lignum
after the Gospel: improvisation on Alleluia Dulce lignum
Credo III
Offertory: Protege, Domine
Offertory selection: Crux fidelis
Sanctus et Agnus Dei: Mass XI
Communion: Per signum crucis
Communion selection: Vexilla Regis
organ improvisation on Christus factus est
Postlude: Fanfare (Kenneth Leighton; English composer, 1929-1988)
Because of its extraordinary beauty and its moderate length, we repeated the Respond of the Gradual Christus factus est. This is in fact the way the Graduals were originally performed, and it creates the symmetrical ABA form. For reasons of length, the repeat was eventually abandoned in practice.
One thing I try to do often, in addition to improvisations, is to include music of the modern era at Mass. It recently came to my attention that a prominent church in London has prohibited any music composed after 1900, and this, if accurate, is a pity. It is tantamount to claiming that there has been nothing of beauty composed in the past 100+ years. I do not call particular attention to the modern pieces, but rather seek to show how they can blend harmoniously with the liturgy. If you're a composer, please do not hesitate to submit your materials to me; I'm always looking for new pieces.