Another thought was Key lime pie. Very American. The recipe I use is from Bon Appetit's best key lime pie ever.
BA'''s Best Key Lime Pie Recipe | Bon Appetit if you're interested. The whipped cream topping is stabilized with Greek yogurt, and you can make this pie all at once or in three stages. No graham crackers over here, but I think I could find a substitute. No Key Lime juice either, though. I don't remember seeing limes. Key Lemon Pie?
Gracie's peach pie and dewilson's suggestion to buy ice cream are looking good. Also very American, and these folks are very inclusive and internationally oriented, obviously. I should take a flag too Bwahaha!