Lauren, if you are flying for Thanksgiving, I would count on a packed flight and that the bag will count as one carry on. Don't be nervous - Attendants are usually pretty nice, they love our cutie pies, and if your baby starts to scratch or make noise, I just give the bag a firm shake and a 'no!' and that quiets them right up. Sometimes, I'll just stick my hand in the bag for a while so they know Mommy is still there.
You are going to have a wonderful adventure together! Think of yourself as jetsetters!