During a police traffic control, as in all countries, you must have the documentation required by the local law.
In most cases this will be a valid driver's licence and papers for the car.
For a foreign lincense some countries (and some US States) require a IDP (international drivers permit/license).
Depending on the situation, a police officer could also demand documentation of citizenship and/or legal status through an National ID or passport.
In the US the last is less likely, unless you run into a control done by the United States Border Patrol, where - as a visitor - a passport may be required.
What may happen to you if you cannot supply the needed documentation will depend on the laws of the local authorities, which can differ greatly.
Assume: no joy will fall upon you.