Plastic baggies work good...Not sure if there's a 100% waterproof saddle bag, but like I said, baggies in a non-waterproof saddle bag is your best bet.
I have tested Ortlieb personally: Back & Front Roller models are waterproof.
They don't have the "covenience" of pockets, but what you put inside stays as dry as when you put it there.
Once you get organized, they work fine. Nothing is more of a pain than having wet contents when you packed them dry.... and that doesn't happen with Ortlieb RollTops.