The only problem is which books to haul around and which books to leave at home. It never fails that I get some inspiration only to discover that I left the appropriate sketchbook behind so I often drag a heavy bag filled with everything just in case the urge hits.
I have always required my students to use sketchbooks and I've gotten used to groaning and dropping grades when they ignore sketchbook assignments. Lots of fellow art teachers have abandoned sketchbooks for those reasons. I believe strongly that sketchbooks are a vital, artistic tool. The more I draw, the better I draw. When I have my sketchbook handy, I am prone to pull it out and make use of idle time rather than spend it playing on my iPhone.
I also love, love, love the attention I get when I am busy doodling in my sketchbook in public. It's great fun to have someone notice, walk over and admire my work.
Today I am teaching a "how to" in sketchbooks to my second year students. Little things like cut a piece of thin cardboard to sandwich between pages so marks don't scratch through pages or never draw on facing pages or keep your book in plastic as you haul it around to prevent it getting dirty and most of all - have it with you all the time like a best friend ready for a conversation.