Speaking of the Hotel Islita, there is no grocery store on site; however, there is a small grocery a very few miles away in the next small town. You would turn to the left going out of the hotel zone, just past the guard shack. It is more the size and idea of a mini-mart and sells other items as well. For example, when we were there, we found wines from all over the world. BUT, I do not think that they carry American food. Also, Samara is about 20 miles from the hotel, a larger town, and somewhere there one would probably see American food.
Get an answer from Hotel Punta Islita, Autograph Collection staff and past guests.