Well when I was in college I carried a backpack around often with as many as five or six books in it. I'm talking thick, large, and heavy hardcover text books. Also in the backpack a number of spiral notebooks, pens & pencils, a slide rule (I'm old ), and before noon my lunch for the day.

Even after leaving college I would still always carry at least a couple of books. One book related to work and another not.

Now days I still read paper books when availability or economics make that the choice, but generally only one at a time.