I would have just ignored him and not made eye contact; if he wanted to escalate it from there then that's his choice.
In California, as a condition of my carry permit, I cannot in anyway incite a person into belligerence and then justifiably shoot him in "self-defense". Pretty much for me my defense must be, "I was a reluctant participant, I was trying to get away".
...and told him essentially that he wasn't going to get his apology...That went over, shall we say, like a lead brick
Not to bag on you too much, but what other reaction would you truthfully have expected from this jerk other that the one he gave?
My advice to you would be to learn a little "Verbal Judo", and use it to deescalate a situation before it gets to the point of violence - being a jerk in return (no matter how justified) will only make things worse.
I think that this is the most important thing that a person with a CCW can learn, is to leave your ego at home, and be comfortable with the simple fact that because you have a gun you pretty much have the last word in practically any argument you are going to get into anyways (that is, of course, if you didn't leave your weapon at home).
As for options:
Cell Phone
Pepper-spray or Tear Gas
Pocket Knife
CLUB steering wheel lock
Mag-lite
Baseball Bat
Pool Cue
Any other non-weapon "weapon" you can think of
And of course, always try to leave a way out when you're stopped at a light - leave space between the car in front of you; drive up on the sidewalk; etc.