As a long time motorcyclist, I have acquired the gear I find to be most functional, through a very complex series of trials and errors. Make no mistake about it, when someone that has been riding for 20, 30 or 40 years offers you advice on gear, take it. Don't go out and try to prove them wrong, it won't end pretty.
Recently I have been riding a 2014 Kawasaki Z1000. Want to know what's most different about it versus my Kawasaki Concourse and Suzuki V-Strom Adventure? Storage. The Connie has wonderfully easy to use saddlebags that can hold the better part of a weeks worth of groceries. The Strom has saddlebags and a top case that can hold, well everything. The Z, well it has a bitchin' ability to roost out of corners and do wheelies--and carry whatever is in your pockets.
For this reason, I went into my garage cabinets and broke out my Aerostich Courier Bag. Perhaps the single best piece of gear I have ever owned. This bag has carried everything, including taking a kitten from Beverly Hills to Santa Monica, camera gear, a transmission for a Harley, books, clothing, groceries and about 2 dozen other weird items over its life span.
The bag just fits your upper body perfectly and seems to hang comfortably on your shoulder no matter what. I strongly suggest you check one out at www.aerostich.com and snag one for your daily commute. This is my second Courier bag, and this one is about 9 years old. They last and work. Just wish I would have bought one before the three backpacks I thought would be better 20 years ago.