This is my take on it:

You're not going to be arrested if you're caught smoking pot, and carrying some (as long as it's still under the "personal use" amount). You will be fined, depending on the cop.

So I certainly can't see you being arrested only for carrying a bong, possibly a fine. Plus cops can't just stop any Tom, Dick or Harry they see walking down the street and search them. They need some sort of reason. My advice is to not give them a reason :thumbsup: