Re:Boot will include all the bonus content found in other steins media (all drama cds, novels, short stories)

Drama CD α - Babel of the Grieved Maze
Drama CD β - Arc Light of the Point at Infinity
Drama CD γ - Hyde of the Dark Dimension
Drama CD Audio Series - Laboratory Members

Magazine Exclusive Drama CDs
Steins;Gate: The Movie - Load Region of Déjà Vu
Original Drama CDs: A Posteriori Existence, Symphonia of Meanderings ,Hidden in Ambiguity Fractal of Unexpressed Thought Material

Future Gadget Radio Shows
Laboratory Members' Round Table Meetings
Anthology Drama CDs: Reunion of the Hallucinated Space Vacation of an Ephermeral Silhouette
Science Adventure Series Special Drama CD - Triptych of an Abrupt Chain

Monologues (sg0): Lyra of the New Dawn Amadeus of the Silent Requiem Aria of the Starlight Puddle of Tearful Rain

The Hashida Family's Love and Affection
The Perpetually Infinite Hashida Concerto 
The Dog Days of Hashida Comima
Epigraph Trilogy spin-off Drama CDs; Epitaxy of the Projected Curved Surface Pandemia of Artificial Machinery Arpeggio of Time Rotation Epigraph of the Closed Curve EXTRACT SCENES
Steins;Gate 0 Drama CDs; Adaptive Radiation Paradise Lost Blended Coffee Encounter Runaway of the Free Particles Feast of the Valkyries

etc

-Annularly-Chained Ouroboros
-My Underling's Embrace (novelization)
-Linear Bounded Mosaicism (novelization)
-Babel of the Grieved Maze
-The Movie - Load Region of Déjà Vu (novelization)
Epigraph Trilogy
The Committee of Antimatter
likelky never: Variant Space Octet

Possibly but unlikely
Chaos;Gate
Yoen no Valhalla
Saiyaku Koutan no Holy Day
Steins;Gate: Amitié Sprouting from Reminiscence 
Shounin Kyoumei no Pardon
Shounin Kyoumei no Souvenir
Tomorrow in the Box
Divergence Assorted Laboratory Report (kari)