The following is a list of Monsanto Companies. It is good illustration of how much of the food supply we take for granted is controlled by Monsanto and other big conglomerates. Much of this food is highly processed and contains unlabelled GMO ingredients, which, if that is what you want gives you a good shopping cart list. If that is not what you want you might consider local alternatives.
Read your labels. You will not find out about GMO ingredients but you will find out about corn by-products that are mostly GMO already and sugar/sodium content that you would like to control. For now, that is about the best we can do.