I use public transport a great deal, and some years ago I started carrying a book with me wherever I went when I could expect a delay or a longish trip. This book became known around the house as my ‘bus book’.
Short Story collections make exceptional bus books – you can often finish a story in a journey, and you don’t have the problems of retaining large amounts of plot information. Whilst not a smoker, I appreciate good short stories in the same way that Oscar Wilde appreciated his cigarettes – a perfect pleasure that always leaves one wanting more.
Another consideration for a bus book is that it should be light enough / thin enough not to make you feel that you’re lugging a tome around with you. Some years ago I had a jacket with fairly wide and deep inside pockets that made it possible to fit a decent novella in, but my current ‘going out jacket’ is just a none-starter in that respect. For this reason the bus book tends to be a working day sort of thing!
And be prepared for a bus book to make the ultimate sacrifice on your behalf, and get itself left on a bus somewhere…