Ethics Question, What Should I Have Done in This Case?

I emptied out the cat's litter box this morning, and as a rule I never keep the used cat litter around the house but take it down to the dumpster the same day I clean. I had the bag in my car when I pulled over to get a box turtle out of the road. Nobody was coming either direction. However, when I returned to my car the very next vehicle to come up behind me was a cop. (Just my luck!) Now, he pulls over and walks up to the driver's side and asks me what I'm doing out there. "Nothing" was my answer. Then he saw the bag on the floor of the car and asks me what I'm 'hauling'. "Nothing" was my reply again. "I'm not buying it!" said the officer and reached in and grabbed the bag. (That's illegal search and seizure by law.) He looked inside, said something about drugs and then stuck his finger into the stuff and then tasted it! While he was then puking over onto the shoulder of the road it was all I could do to keep from laughing, I had to actually bite my lip! Now, I try to be very humble and nice when dealing with people but should I have gone overboard in trying to stop this guy when he was carrying a loaded gun and was being very rude and forceful?