It depends on the person at the gate, but in general the answer is No. I once had a United person tell me my small fanny pack around my waist was a 3rd item and I would have to remove it and put it and the contents into either my backpack or the computer bag! She turned her back to continue checking tickets during loading. I walked onto the plane.I was thinking since the bag would not be much larger than a large beverage, which is allowed to be carried on, it may not be considered a "bag" or "personal item." It doesn't seem much different than putting in the pocket of a vest, which some have reported works. Another possibility would be to attach it to the outside of the carry-on camera bag. In that case it might not be counted toward the size restriction, although it would be counted toward the weight restriction.
Sometimes you can carry a camera and lens around your neck.....but then you have the camera swinging around as you juggle the other pieces of carry on.
Less risk by following the rules. They typically do not weigh carry ons. One carryon should go in the overhead and the other under the seat in front of you.