And, no -- he cannot search the bag because you told him there's a weapon in it. If you told him it's in the right-front pouch, he is allowed to open ONLY the right-front pouch, and ONLY for the limited purpose of removing (temporarily) the weapon he has been told is in there. He does not get to search even that pouch beyond that. Obviously, the plain sight rule applies, and if you carry your stash of weed right next to your carry weapon you'll have a bit of 'splainin' to do, but telling the officer where to find the gun is not giving him consent to "search" anything.
Unfortunately again, everyone needs to brush up on the law. A cop would actually be justified in frisking the entire vehicle if a weapon is found in one location. After all, case law has upheld that if there is one weapon in the vehicle then it would be reasonable to argue that there could be another. It's no different than if I happen to find the stash of weed next to the gun when I pull it out. I not only get to seize that weed, but I have probable cause for a warrantless search (carrol doctrine) of the entire vehicle. So yes, way more than the right front pouch would be in play. This does not apply to just the area around the front seat, it would include the entire lungeable area inside the passenger compartment. The lungeable area in a vehicle, MOST OF THE TIME, would constitute the entire passenger compartment. Trunk and engine compartment are out of play. Again, if you give off no indicators of being a bad dude you likely will not get your whole vehicle frisked. I know I wouldn't do it. Honestly I wouldn't even worry about keeping the gun for most people that are straight enough to tell me about it as long as they have their CCW permit... other than that "I've never met you before and don't know you" factor. And yes, EVERY traffic stop is indeed a criminal investigation. It may be for the simple crime of a burned out tail light, but that is indeed a crime in most states. It could also, there again, be for the crime of bank robbery if you're in the wrong place, wrong time, and look like the guy.
It should be noted that some states place greater 4th amendment restrictions on LEO's than the SCOTUS has. That's great. States can be more restrictive (on LEO's), but no less. Per federal (and my state's) case law, the above applies.