Aer Lingus carry on requirements?

This fall I am going abroad for a semester. I am flying American Airlines from Chicago to London and then flying Aer Lingus from London to Shannon, Ireland. I know that American Airlines allows one carry-on item (like a small suitcase) as well as a personal item (I'm hoping to bring a backpack). However, from... show more This fall I am going abroad for a semester. I am flying American Airlines from Chicago to London and then flying Aer Lingus from London to Shannon, Ireland. I know that American Airlines allows one carry-on item (like a small suitcase) as well as a personal item (I'm hoping to bring a backpack). However, from what I can tell, Aer Lingus only allows one bag per passenger in the cabin. Will it be a problem if I have a suitcase and a backpack with me on my Aer Lingus flight? I'm trying to make the most of my luggage space and I don't really want to check another suitcase.
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