I always take one or two small books altho I seldom get a chance to read and sometimes in 10-14 days do not even open them up.  The subjects have to do with where I am at, what I am doing, like wildflower guide or some fur trader's journeys along the MN/Ontario border, etc.  I have taken larger books but between the weight and the fact I might never get around to reading, I've given that up.