I have in mind something I can put up on my shoulders or around my waist. Not necessarily to strap it on; something I can doff at will, but that will stay secure, like shoulder hooks or something. In transit, I want my hands free to be able to other things, or carry other things, whatever. But I don't want to be unable to drop the cart and run or dodge if I have to without undo manipulation.

A cart makes a lot of sense, especially in an urban environment that is for the most part still intact. Even in rugged terrain it could be helpful, but within limits. Maybe there'd be a way to rig up something you could pack on your back if you had to, and when the going is a bit easier you can put it down on integral wheels.