Yes, basically.
Traffic stops are a bit more problematic, however. In some states, you can be arrested for offenses that do not carry jail time as a possible penalty, and this gives the police a back door to search your car and any containers contained therein, excepting locked containers in the trunk.
Additionally, the "protective sweep" doctrine was recently expanded by the 5th Circuit, though it is unclear whether this will survive SCOTUS scrutiny. As far as "keeping your private stuff out of sight," the protective sweep jurisprudence makes it clear that police can briefly inspect any area or enclosure which could contain a person.