Plastic zip bags are rare creatures in Germany. I'm not sure why, but Germans do tend to be a little wary of plastics leaching undesirable chemicals, as well as landfill and use of resources. They do have other kinds of plastic bags, so this lack of zip bag adoption is still a mystery to me (as well as their slow adoption of the slow cooker).
But there are several arguments in favor of the zipper bags. They are sanitary, they do not leak during transportation, they are compact and fit into a refrigerator more easily. You do not have to mix the cutlets, you just flip the bag over to stir. They also save water by being disposable. So feel free to break with tradition and use a gallon size zippered bag for your German feast.