A surgeon told me dry buiscuits to keep the acid down. Before my op I would keep some dry crackers in the car and eat one every hour or so. Even as a passanger you are burning up energy (nervouse energy) and the stomach reacts. I carried a few cream crackers and ate them dry. Too much gaviscone can make you constipated. Not necessarily good for all cases of reflux. Lots of foods are antacids just as some are likely to give you more reflux. Working it out logically, when you are sitting your stomach is squashed up, pushing the contents and acid up, the sitting position in a car is not natural because you are still using legs agitating stomach. Using a Dry buiscuit is dampening it down. Watch the calorie intake and cut down main meals accordingly.
Not a doctor, just an old one who has had to find out the hard way. x