Very general, basically for every airline I might be flying with: Is it possible to bring a camera backpack and a separate thin notebook/mesenger bag for a 15" notebook?
Basically I'm looking to buy a new camera backpack, and I could chose one with a notebook compartment, but then I'm carrying this extra weight for a bigger backpack and the compartment around with me while I'd only need this compartment when actually traveling.

Are there airlines that won't allow the additional notebook bag as carryon luggage?