In order of contribution:
Logos: While not writing anything personally, his Laws of Physics, carried over from the previous World, were the first to be written on the Universal blueprint, and all other details which followed were built upon those Laws.
Teknall: Aside from Logos, Teknall's works have formed the foundations of the blueprint. As a special addition, Teknall has also added fantastical elements (including, but not limited to, Adamantine and Mithral).
Toun: Another major contributor. Toun's biggest focus was allowing the Universe to foster life.
Vestec: Vestec's additions, done with intent of vandalism, included the crazy and unexpected, such as space monsters, asteroids where they shouldn't be, too big suns, too small moons and fracture planets.
Vulamera: While not making any unique additions of her own, Vulamera accomplished the important task of unifying all of the additions into a single, cohesive whole.
Mammon: Mammon has inserted the means of the occult into the Universal blueprint, from ingredients for alchemy and rituals to secret words of power.
Vakarlon: The Trickster has added an element of chance and luck to the Universe-to-be.
Julkofyr: Down at the quantum level, this god of Shadows has obscured the properties of things at this scale and made them uncertain (effectively, quantum physics as we know it). Julkofyr has also ensured the existence of the vacuum of space and the void between atoms.
Zephyrion: This god of Air has asserted his dominance over his Domain by rewriting the gases to his will (effectively making them the reactive, diatomic gases we know now). More significantly, Zephyrion has imbued the blueprints with the Winds of Change, ensuring that the Universe will forever be a dynamic place, never at rest.
Niciel: Niciel timidly made a small contribution, adding some of her purity to balance out the chaos and suppress some of the disorder.
Astarte: She has added a touch of her own essence, imbuing the Universe-to-be with her magic, potentially allowing for impossible, magical features to appear such as flying rocks, living dirt or, at a bare minimum, magic users.
Slough: Her accidental touch has ensured that the Universe-to-be will be perfectly palatable for life of all kinds.
Belruarc: She has added her own magic, a lawful, scholarly magic, to the Universal plan.
Jvan: The All-Beauty has filled the gaps in the plans with otherworldly, eldritch, organic beings, which would live just outside the Universe, waiting and watching for wherever the wall of reality grows thin enough for them to intrude.
Notable works which were not part of the blueprint include:
Reathos: Reathos has become keeper of the Primordial Pool, the place where spirits go when their hosts die, and maintainer of the cycle of life, death and rebirth.
Illunbar: She made her Dreamweaver, making Dreams something special. This is not written into the blueprint, although it borrows from its power.
Slough: Unwittingly, she has become the progenitor of all natural life in the Universe. While the blueprint contains some facsimiles of life, and it provides a hospitable and fertile place for life, it is by Slough's essence that the Universe will be inhabited by life.
Ull'Yang fed his arm to Slough, but is otherwise yet to contribute. Vowzra is yet to contribute, although that contribution has been promised to happen at the very end. Kyre and Daegon have also not yet contributed anything.