There is one "Exclusive" CB channel, that is Channel 9, which is reserved for emergency/priority traffic only (Calls for assistance) The remaining 39 are first come first serve.
Truckers, by tradition (originally by mutual agreement) hang on Channel 19, which makes it the best palce to be if you are on the freeway..
Good Sam claimed 13 for RVers, not just Good Sammers but ll RVers, still kind of dead.
11 is often a "local calling" channel.
But save for Nine, they are all first come first serve.