Carrying a hardcover book van be helpful for many reasons. For your reading purposes, as a table for your laptop and as a document holder (a book will keep your documents from wrinkling up). A hardcover book could also make for a decent weapon if you use it right! For leisure, work and sudden attacks, a good book will cover all your needs.
Notebook + Pen
More people than journalists and other creatives should carry notebooks, as it will keep you looking for good stuff to write down. Be it a slow poem, a witty quote or a quickly scrambled down address; your notebook will have some of your everyday-life in it. Sure, your phone has a notes application, but your battery will die when you need to capture something important! Keeping your thoughts in ink will make it more permanent and great to reflect on later. Don’t forget the pen!.