You must have a Permit/License to carry a loaded handgun in any vehicle. CA does not issue non resident permit/licenses and does not honor any other states permit/licenses.
The transportation or carrying of any pistol, revolver, or other firearm capable of being concealed upon the person by any citizen of the United States over the age of 18 years who resides or is temporarily within this state, and is not within the excepted classes prescribed by Penal Code Sections 12021 or 12021.1 or Welfare and Institutions Code sections 8100 & 8103, provided that the following applies:
1. the firearm is within a motor vehicle and it is locked in the vehicle's trunk or in a locked container in the vehicle other than the utility or glove compartment,
2. and when the firearm is carried by the person to or from any motor vehicle for any lawful purpose, the firearm must be contained in a locked container while being physically carried. (Penal Code § 12026.1.)
Also CA has magazine bans. Bringing them into CA could be a crime.
Large Capacity Magazines
With limited exceptions, California law prohibits any person from manufacturing, importing into the state, keeping for sale, offering or exposing for sale, giving, or lending any large capacity magazine. Cal. Penal Code § 12020(a)(2), (b). A "large capacity magazine" is defined as any ammunition feeding device with the capacity to accept more than ten rounds, but does not include any .22 caliber tube ammunition feeding device, any feeding device that has been permanently altered so that it cannot accommodate more than ten rounds, or any tubular magazine that is contained in a lever-action firearm. Section 12020(c)(25). California does not ban the possession of large capacity magazines.
Upon a showing of good cause, the California Department of Justice may issue permits for the possession, transportation, or sale of large capacity ammunition magazines between a licensed California firearms dealer and an out-of-state customer. Section 12079(a). This requirement applies for only the out-of-state importation and exportation of large capacity ammunition magazines, including the transportation of such magazines as necessary to complete a transfer to or from an out of state source. See Cal. Code Regs. tit. 11, § 978.40.
Large capacity magazines may be manufactured for any federal, state, or local government or law enforcement agency, or for use by agency employees in the discharge of their official duties, whether on or off duty. Section 12020(b)(30). Large capacity magazines may also be purchased or loaned for the sole use as a motion picture, television or video prop. Section 12020(b)(31), (32)(A). Such magazines may also be resold to law enforcement agencies, government agencies, or the military, pursuant to applicable federal regulations. Section 12020(b)(32)(C).
For additional large capacity ammunition magazine regulations, see Cal. Code Regs. tit. 11, §§ 978.40-978.44.
Whats the point of an Amendment if it isnt followed or ignored.