Complex sentence: His cousin's girlfriend had accidentally taken his keys to Los Angeles and Bryan, wearing the boxers and shirt that he had slept in, had to drive there to pick up the keys, and then drive back to Ventura to pick up his car and brother.
Split into simpler sentences: His cousin's girlfriend had accidentally taken his keys to Los Angeles and Bryan, wearing the boxers and shirt that he had slept in, had to drive there in order to pick up the keys. He then would be forced to drive back to Ventura to pick up his car and brother.