Itinerary books have always been traditionally produced on copiers or mopiers. As such, they have generally been designed to work with standard copy paper sizes — 8½” x 11″, 11″ x 17″, and so-on. The standard itinerary book you have on your desk right now is more-than-likely 5½” x 8½”. Back in the day, the binding would either be a 3-hole punch to fit in a loose leaf binder or a “GBC”-type plastic comb. More modern bindery techniques include hot glue and the most common plastic spiral binding. (Yes, we know it’s a helix, not a spiral.)
That is not to say that these are the only sizes and binding types, just that they are the most common, and least likely to require the reinvention of the wheel.