We have always been able to offer just about any piece of literature we wanted to, as long as it was published by the "Mother" (a.k.a. "Organization"), and as long as it wasn't anything too old (for example: Russell's or Rutherford's books). However, if you wanted to offer only the Bible to householders, it wouldn't be very long before you were questioned about your motives by an elder or an overzealous nosy pioneer sister. Most would be peer pressured into going along with the "suggested" literature offer.
I have often only offered Bibles, certain tracts and brochures. But it is difficult to have a quantity of Bibles and carry them in your service bag. Plus the literature counter only stocks so many at a time.
If you've ever read the old "Kingdom Ministries" from back in the 20's, 30's, and 40's, (called "Bulletin" and "Informant"), it is easy to see how it was all about movement of printed matter. It was even more obvious in those days.