I read an article some time ago about what foods in particular you should purchase organic. I could not find that article specifically. However, Prevention has a very informative article about twelve plants to buy organic and fifteen that are naturally clean. Then, I found this chart on my renewed drug of choice - Pinterest.
Chart via here
Of course, I suggest you purchase your fruits and vegetables with reuseable produce bags.
Don’t forget to eat your fruits and veggies and be good to Mother Earth.