Many of us wear the Aeronaut on our back with a Synapse on front. Here's an example with my Brain Bag on my back. Fully loaded, it gets heavy and can throw off my balance a bit, but it all works out. If standing in a long line, I usually end up grabbing the Synapse top strap with both hands (like my left hand is doing here) and resting my chin on it.
Not saying you'll win for style points with this method, but I much prefer it to carrying a bag with the shoulder strap or just in my hand. Let's hear it for TMNTS! (And I look like a goob in this picture, but whatever ... the things I'm willing to do for TB!)