A pilot must carry a government issued photo ID, pilot certificate, and medical certificate.
When exercising the pilot privileges as a required flight crewmember, the pilot must have in physical possession, or readily accessible in the aircraft, a valid pilot certificate or special authorization. In addition, the pilot must have photo identification. The identification can be state issued such as a driver’s license, or federally issued such as a U.S. Armed forces ID or passport. The pilot must also have a valid medical certificate for the level of pilot privileges being exercised.
14 CFR 61.3 Requirement for certificates, ratings, and authorizations.