They do have rolling luggage that fits overhead. That and a laptop briefcase/shoulder bag should be OK. I personally like backpacks. I'm nearing 30, and still feel it's fine. I think as long as you're not wearing a full suit, a backpack is understandable on an airline. If you are in a suit, take the jacket off!

Or you could still duffle, sling over shoulder, and carry the laptop in the other hand? I think that, unless you're strapping things on to you, you'll still have both hands busy.