I don't know if it's perfect, but after lugging a backpack around for four months I'd had enough, the backpack wasn't doing the trick. So, one afternoon my little sister came over to help with the kids while I did an all-out internet search for the most functional and economical bag I could find to tote around my mothering accoutrement.
My requirements were simple: A. I needed a shoulder strap that was long enough to go across my body-messenger bag length. B. It needed to be big enough for my personal effects, cloth diapers and wipes, extra underpants for Luke and space for sippy cups and a water bottle. C. It needed to look not lame.
I settled on this discontinued model Vera Bradley messenger bag. It met all my requirements and is a little funky without being overtly feminine (after all, I have two boys). It's funny though, because I picked this pattern based on the low price, and now a few weeks later it's now considered a 'collector' and costs more than a new edition pattern. Of course, mine won't be a collector, it's already worn with old fruit snacks and spit up.
The search is over...for now. Thank you for all your input!