My personal opinion: don't ask, don't tell. If he didn't ask if you have any weapons in the car then you don't need to tell him. If he did ask, then of course be honest with him and also inform him that you have your permit. It really depends on the officer as to how they react. I have been pulled over twice on my motorcycle not carrying a firearm, but had a pocket knife on me. One time the officer reached in my pocket and took it "for his safety" and the second time a different officer said he expected all guys to carry a pocket knife and didn't think twice about it.
Hmmmm... I have 1/2 inch pocketknife on my key chain. If I am asked if I have any weapons in the car I'll fess up to having it and show it to the LEO. That will get a good laugh and direct his attention away from any other potential items.