I'll ignore the moral policing going on in this thread.
But word of advise to the OP, this is Pakistan. As you can see even in this thread, many people disapprove a girl and guy sitting in a car and having their meal and in an instant they start thinking about all kinds of exotic stuff (haraam kaam!) that must be going on in the car. Then you can imagine how some Policemen may perceive this situation.
Under law, there is nothing these policemen can do against you. However practically, you may encounter any kind of policeman depending on your luck. Most are there just to make some easy money by scaring a young couple (the ones you encounter belonged to that category). However some may be illiterate goons that would bully you and may go to any extent in harassing you or the girl - think of encounter specialists sort of. It's better to avoid arguing with the latter type.
Best way to deal with this situation is, as mentioned by a poster above, just remain confident when meeting them. They will judge whether you were doing something fishy or not by your confidence and the way you greet them. Remain calm but assertive. And then negotiate like you negotiate with a pathan selling smuggled goods.
Legend is that once a policeman or warden stops you, you cannot get rid of him without paying something. Consider it as sadqa and don't think too much about it because well this is Pakistan aur yahan sab chulta hay.
