"You don't have to answer any questions as a passenger. Just say 'I don't answer questions.'"
Berkemer v. McCarty (1984) held that roadside questioning during a routine traffic stop is not a custodial interrogation for Miranda purposes. That means the officer does not have to read you Miranda rights before asking questions. It does not mean you are required to answer.
Hiibel (2004) held that a state may require you to disclose your name if there is reasonable suspicion that you have committed a crime. It said explicitly that no physical ID document is required — only a name, and only where reasonable suspicion exists as to you.
The result: you generally do not have to answer questions, but the officer generally does not have to tell you that, and in some states refusing to identify yourself is itself a crime if there is reasonable suspicion.