I suggest a diaper bag, preferably with a hazmat symbol on the side. Range bags and tool bags are great, but they scream "valuable stuff waiting to be pawned." If you have to leave one in the car, it could attract thieves. I don't know of any dirty diaper thieves, though.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.