Thus far in my car-lite lifestyle I've been using a cardboard box bolted to my rear rack. Its worked well but I've come across a few security concerns in the past. So I've been giving some serious consideration to using a backpack even though I detest having anything on my back while I ride.

Does anyone have a system they use?? A pack would be nice as I can take it into a store and keep all my valuables handy. But then its one more thing I need to worry about.