A photograph of the Daemon (before he was a Daemon, though there are still some features recognizable in the photo) shaking hands with the Emperor.
One of the Immortal Sensei, bound within a chamber by terrible wards and forced to play poker (or Cribbage, Uno, Jenga, etc) with the Daemon.
A mangled (but repairable) suit of Squat Exo-Armour.
A Warrant of Trade with the Emperor's signature in blood (from Matt Farrer's 'Legacy').
A complete set of Lincoln Logs (very, very old).
A piece of what appears to be a savior pod's hull with the letters A.S.A. on it (it appears the first letter has been obliterated by horrible scorching).
Goge Vandire's baby rattle.
A complete and unabridged account of the Horus Heresy, spanning 369 monstrously-sized volumes, all in the same handwriting, authored by "Malcador".
A massive collection of finely sculpted figurines representing Astartes, Sororitas, Inqusitors, Lesser Daemons, all with individual names stenciled on their bases and sculpted by the Daemon, representing his kill tally.
A detailed star chart and map painted on the ceiling in blood and other unidentifiable medium showing the exact route of one particular Black Ship, including it's secret path into the Sol system.
A Remembrancer's "press badge" (Ander Cooperson) allowing unrestricted access to chronicle the Victory of Ullanor.
One of those memory games, with the pictures on the tiles representing the Primarchs (four of the tiles are missing).
A hanging mobile, including every (horribly twisted, melted, and blasted) individual component of a Shadowsword Super-heavy Tank (crew optional).
A gold snuff box with the initials D.H.H. engraved on it (purported to belong to a long-dead Inquisitor of the Ordo Hereticus).
Hope this helps.