Not a lawyer, just a guy who’s been pulled over way too many times for no apparent reason.
They always have a reason, a bank was robbed, someone hit a pedestrian, a white car was seen fleeing an accident, some of them might even be true but my point is the reason they stopped you isn’t where you want to put up a fight.
The same goes for license and registration. Technically you need both to operate the car, so you’re breaking the law if you can’t provide them. This would be something to fight in court if you wanted to, not by the side of the road.
My understanding is that any searching they want to do beyond that would require some kind of cause or permission on your part. This doesn’t cover anything they can see outright. You should probably still be polite, but you can decline to let them look through your things.
They may decide to do it anyway and that’s something you would have to talk to a lawyer about your specific situation if they find something.
I’ve always been polite, always asked questions, and I’m always amazed at how sure they are that I’m a criminal, even with nothing heavier than a speeding ticket on my record.