On top of knowing the laws, if you do get pulled over, maybe shutdown and stow the gear. Just because something may be legal, it won’t stop a cop who’s less than honest from lying to you and trying to cite you or take your gear.
Lying to you about what?? I realize that the laws in California are different than anywhere else in the country but a cop isn't going to write a ticket for something that's "not on the books." Furthermore, I don't believe any cop is going to jeopardize his job by trying to "confiscate" a scanner.
And the others are right. Make a few movements in the vehicle when the officer stops you. I can all but guarantee that you'll extend the length of the stop.