I know the decade of the backpack purses have long passed us, but I liked the convenience of having my hands free while shopping. Especially at outdoor markets and craft fairs.
I did find this cute little courier-like bag at Osprey Backpacks. It has the storage features of a backpack and the strap length of a messenger bag. So you can remain hands-free and still feel like your stuff is secure. Insert immediate flashback to the movie Burn After Reading. "I thought you might be worried about the security of your &!#!"