instead of salty snacks or high calorie ones, try granola bars, peanut butter crackers, diet sodas, or fruit juices, water. if they eat at truck stops, hit the salad bar, and order foods either baked or broiled, stay away from all you can eat buffets, and maybe park far enough from the building that they have to walk a few minutes to get inside.
but "all your drivers", frankly no matter how many you have, you cannot force them to live thier life, your way.
driving your truck is one thing, personal habits are another.....