Honestly, your not going to fly that plane very long so just get what ever bag you want because you could pack it in a suitcase and it will still fit in the clost . Only one of the pilots has to have their GOM/FOPM/CFM in the cockpit. All of our FO's just grap their headset and Jepps out and leave the rest behind the seat in the closet. I have been ramped before and the guy never said anything to me about both of us having those books up there.
Well, like the other guy said though enjoy the flying because the pay will suck but it will be the most fun you will have flying for an airline. I have the the 22" rollaboard from PNG and it works great. You can either put it in the AFT cargo or in the closet. There really is plenty of room in the closet for your stuff.