Since the OP used to fly for an airline, he's seen the LuggageWorks rollaboards, but not everybody knows that they sell extra clips that you can have sewn on to another bag.

So the rollaboard can carry the flight bag on the j-hook, laptop bag or backpack on the top against the handle, and a large duffle bag clipped on the top and resting against the flight bag. So everything is one unit instead of dragging around two.

As far as what to pack, I'd consider dumping things like cotton t-shirts in favor of Under Armour, ExOfficio, etc. Clothes made out of technical fabrics are much more packable in addition to being easy to wash in a sink if needed and way more comfortable. SmartWool lightweight merino wool socks are great, too.