Couldn't one build a device which will take USB power, but not data.
I.E. - have a device that you plug into the end of your cable which will filter the data off the connection such that juice jacking is impossible. You plug one side into power - it pulls in the power, and then feeds data-less USB power out the other side...
Yes, this is the by far the most common answer. However, one would need to remember to bring said special cable, which at that point why don't you just remember to bring the wall wort USB adapter instead of carrying around a charge only cable?
Side benefit: wall wort USB adapters can push more amps to your device (e.g.. faster charge) than USB hosts.
I.E. - have a device that you plug into the end of your cable which will filter the data off the connection such that juice jacking is impossible. You plug one side into power - it pulls in the power, and then feeds data-less USB power out the other side...