The officer who stopped you may try to trick you into revealing incriminating evidence, banking on you to be panicked and flustered. He may ask you if you have anything illegal or anything that could be considered trouble in your vehicle, and he is counting on you to respond out of a sense of cooperation or fear. However, you have no responsibility to respond, and you never have to volunteer information that could get you in trouble. If you have contraband in your car, or you are on your way home from the bar, you should definitely keep that information to yourself.