Mears shuttle won't allow you to bring luggage on their buses between US/IoA and WDW. We asked and were told we could bring backpacks.
How are you getting to your US resort from the airport??? You can rent a car at the airport and keep it until you arrive at AKL..but keep in mind that you will be paying to park at your US resort....about $15 a night now.
You can also hire a car service to cart you around as well. Or just take a cab each time. Price 'em out and see which meets your needs the best.