Because of the mobility of cars, the rules for searching vehicles are less restrictive than searching a residence. That doesn't mean anything goes. There are times when a search warrant is required and probable cause must exist for the issuance of probable cause. Roadside stops create issues which don't necessarily mean the right ot search, warrantless, exists in all cases. However, if the driver or car occupant can be arrested, a search incident to arrest may exist. For instance, DUI. If another licensed person is at the scene, typically a non-intoxicated passenger, the car can be driven away without a search if the car is in safe, drivable condition. A lone driver dui may justify a warrantless Inventory search where the car is to be towed to a holding compound. Inventory searches are permissible to forestall allegatrons of valuable items being stolen from the car while in police custody. Warrantless searches of a vehicle are permissble when the officer has probable cause to believe that a crime was committed by an occupant or drlver. For instance, a speeding car is stopped. A cloud of sweet smelling smoke engulfs the officer when a window is rolled down. The officer is familiar with the smell of marijuana. He can then search the car for marijuana and if he finds any marijuana or over the limit ducks, any found contraband is admissible evidence.
A judge gets to determine the credibilty of the reason for arrest, however. Another justifiable search: Game Warden sees more ducks fall out of the sky than a limit or hears an unplugged gun. He sees the party go to a vehicle and put something in the trunk. No ducks are visible at the car. He has probable cause to search the car because he has probable cause to believe there was a game violation. If you are hunting, as Gene has said, a game warden is permitted to ask for and check your license and gun. The worse thing one can do in some jurisdictions is to be caught lying about a material fact to a leo acting in the performance of his duties. This sometimes can be a felony under both Federal and some state laws. Lying to cover up what would be a misdemeanor offense game violation can in some cases imperil your 2nd amendment right to have a gun.
