Though it may exist, i'm unaware of a Traveller version of "Appendix N" -- a recommended reading list, providing a list of authors whose works inspired the development of our favorite science fiction role playing game.
I've mentioned in the past that I was fortunate to come across a large collection of old paperback fiction. Not all of it was of the swords and sorcery variety. I also obtained some old science fiction novels from the 60's and 70's. One of those novels was Ensign Flandry, by Poul Anderson, which was published in 1966. This is not the first published Flandry novel, but comes earliest in the chronology of the series.
If a Traveller Appendix N does exist, I imagine Poul Anderson's Flandry series ranks as one of the more significant inspirations. Here are a selection of quotes from Ensign Flandry, which may have been inspirational to the Traveller designers.
"Everyone knows the Empire was won and is maintained by naked power, the central government is corrupt and the frontier is brutal and the last organization with high morale, the Navy, lives for war and oppression..."
"The sky illumination had now formed a gigantic banner overhead, the sunburst alive in a field of royal blue..."
"They crowded into the flier. It was a simple passenger vehicle which could hold a score or so if they filled the seats and aisle and rear end. Flandry settled himself at the board and started the grav generators."
"People say 'hyperdrive' and 'light-year' so casually. They don't understand. A series of quantum jumps, which do not cross the intervening spaces, therefore do not amount to true velocity and are not bound by the light-speed limitation..."
"'Lord Hauksberg is continuing to Merseia in another couple of days,' said Commander Max Abrams, of the Imperial Naval Intelligence Corps. 'I'm going along in an advisory capacity, so my orders claim. I rate an Aide. Want the job, Ensign?' Flandry goggled. 'You've shown yourself pretty tough and resourceful. A bit of practical experience in Intel will give you a leg up, if I can convince you to transfer to the Intelligence Branch.'"
"The starship Dronning Margrete was not of a size to land safely on a planet. Her auxiliaries were small spaceships in their own right. Officially belonging to Ny Kalmar, in practice, a yacht for whoever was the current viscount. She did sometimes travel in the Imperial service: a vast improvement with respect to comfort over any Naval vessel. Now she departed orbit and accelerated outward on gravitics. Before long she was clear enough into space that she could switch over to hyperdrive."
"The ship whispered. Powerplant, ventilators, a rare hail when crewmen passed each other in the corridor."
"'Come, come,' Hauksberg said. 'A galactic government is impossible. It'd collapse under its own weight. We've everything we can do to control what we have, and we don't control tightly. Local self-government is so strong, most places, that I see actual feudalism evolving within the Imperial structure.'"
Well I could go on, but I think you see the picture. The Ensign Flandry series is not the only science fiction source from which GDW may have drawn, but it certainly captures the flavour of many of the Traveller game elements, such as character generation, assumed setting, equipment, organization, starship design, and government and nobility.
Edit: You can find a recommended reading list from Space Frontiers on Dennis' What a horrible night to have a curse blog.