If you make a variety of sandwiches for your family trips it can be disappointing to bite into the wrong one. Real Simple magazine's weblog suggests that you label rubber bands with the type of sandwich and wrap them around the paper or bag.
The benefit of this method over just labelling the baggie or paper directly is that if you frequently make sandwiches you can reuse the rubber bands easily. Some people do reuse sandwich baggies a few times but you can use the same rubber band label for years.
Rubber Bands as Sandwich Labels [Real Simple]