Your personal item, yes. Your rollaboard bag, no. If you're not familiar with it, your personal item has smaller allowed dimensions than your main "bag"; examples of personal item are a laptop bag or a smaller backpack (I have a photo+laptop backpack which can barely hold my 14" laptop as well as a camera and several lenses, and it's right at the limit of the personal item size). And, as mentioned above, your personal item has to fit completely under the seat in front of you, with no protruding straps/etc, in an exit row on AA.

And be aware that the horizontal space under the seat in front of you can vary, depending on which type of 737-800 you have. If you have the 737-800 with in-seat AVOD, then the window and middle seats have entertainment system boxes taking up some of the space. But the aisle seats start with less space, no I'm not sure if you end up with any more net space in the aisle seat than in a window seat with the entertainment system box. But AFAIK there's no way to tell whether you'll have the 737-800 with or without the in-seat AVOD; On the LAX<->BNA nonstop route, for example, it tends to alternate between the two types of 737-800s (which both have the same seating chart AFAIK). Whether it has AVOD or not depends on when AA ordered the plane, no it's a difference of vintage, not model.