How many of the following can you check off your list to form at least a mediocre human being?
History: At the very least, a broad overview of Egyptian, Phoenician, Hebreaic, Heroic Age Greece, Roman Republic and Empire periods, and the history of Western Europe from the Dark Ages to today. Given current world events of the last decade, special focus on the origins of Islam, it's original spread and resistance thereto, and the origins of the newer more radical movements (Qutb particularly) are well worth getting a grounding in.
I'd personally suggest supplementing the above by finding some historical reenactors in your area and/or western martial artists and/or a modern soldier up on his doctrine and military history. Not necessarily for the art itself, but to better understand the mindset of the people doing the fighting - since so much of human history has been fighting, sadly.
Economics: Smith, Keynes,Marx/Engles, Friedman/Hayek - know at least the names and summarize their views.
Literature: Work through any 101 or 201 syllabus prior to 1960 or so... the Big Milestones are usually Beowulf, Chaucer, a couple Shakespeare plays and sonnets, maybe Milton or Donne or Spencer.. then a couple Romantics like Byron or Blake, and a 19th c. novel or three. I'm not overly fond of Dickens, but he was popular and gives a decent feel for the age. Maybe Doyle would be more fun. :~
Humanities: "History of Art" and "History of Music" 101 level.
In both literature and the humanities, I'd definitely stick with canons put together prior to the PC era. Not because there aren't great and important works done by people of all manner of minority status, but because you're looking for fundamental milestones in the art - and modern canons frequently give short shrift to the latter so as to give more time to the former.