Let me start with this is not a pissing contest. It’s not meant to drive people to buy things. This is just a list of suggestions of material that, directly or indirectly, have been a part of gaming from the beginning.
I will be listing not only the well known, like the white box or brown box, but the other gaming aids, books that influenced the original D&D creators and links to articles on the web that cast light on the many aspects of the hobby that many of us grew up with and for those just trying out the material for the first time.
You don’t have to buy any particular version of anything. Rather than buy a book printed in the early ‘70s and high priced as a collectible buy a recent edition that may have additional content and save money for another item. Or even pdfs. Many older sources are freely available on the web and can be downloaded from Gutenberg and other classic fiction and non-fiction books from Lord Dunsany, Edgar Allan Poe, H.P. Lovecraft, Edgar Rice Burroughs to historical material, ancient maps and more. The bookshelf can be virtual as well as physical.
The hobby grew itself in much the same manner until the mid-late ‘80’s when the trouble began between the ‘hobby’ and the ‘industry’, so there will not be much in the way of historical material covered past the end of the ‘80s, only newly created material (house rules, conversion notes, etc).
I hope this helps and if I miss something or have been misinformed about something please leave a comment.