I thought I'd put together a little guide for shopping, for anyone trying to eat a healthier diet but is having trouble figuring out what that means.
First of all, whole veggies, fruits, fish, and meats are easy. No ingredient list. What you see is what you're eating. With that said, try to avoid corn and potatoes when in the produce section, and fruit should be more like a treat than a staple. Corn because it's a grain, and starchy; potatoes because of the high starch content; and fruits because of the higher sugar content. Also, if you're suffering from an inflammatory disease of some type, such as arthritis or fibromylgia, try to avoid the nightshade plant family as well (peppers, tomatoes, potatoes, and eggplant. Peppers means the vegetable, not peppercorns.) For meats, if possible, try to get grass-fed or pastured, rather than grain-fed; similarly, wild fish is more nutrient-dense than farmed fish. Grass-fed meat has a much higher omega-3 content, a vital fatty acid that most people in the US don't get enough of. Also keep an eye out for frankenmeats, whether cured (bacon) or a hodgepodge (sausage). There are often unknowns in these, so take a look at that ingredient list before buying.
Once you have all the whole foods you can eat, let's move on to dairy. Plain cheeses rarely have anything added to them, but the flavored ones often do (we saw a goat's cheese with high fructose corn syrup in it yesterday. Ick.) Get whole milk rather than skim - the fat is necessary to actually absorb that fat-soluble vitamin D. Look out for preservatives in your cream. Garelick Farms has an 'all-natural' line that I like, and any organic brand won't have any extras. Check the ingredients list on yogurts, sour creams, etc. too. Many of these have added sugar. Again, go for the regular stuff rather than low-fat or skim; vitamin D isn't the only fat-soluble vitamin out there. Here, too, grass-fed or pastured is better, if you can get it.
Next, skip the bread, chips, pasta, canned veggies, soda, and cereal sections. Just walk right past them.
For everything else you might want to buy, check the ingredients list for the available brands. Buy the one with the least high fructose corn syrup, fewest unrecognizables, least sugar, and the least soy. Some of those might surprise you; you'll find that mustard is easy, but there aren't many ketchups without HFCS. You'll also find that the store brand is sometimes the healthiest choice. If you like nuts, macadamias have the highest omega-3 content, while walnuts are mostly omega-6, and almonds between these with a fairly neutral balance.
I also recommend learning to make your own mayo and salad dressings. It's not all that hard to do, and that way you'll be able to avoid the soybean oil these products are always made with.
One more note: Here are some good resources if you are interested in joining a veggie CSA or a meat share. Local, small farms often have more nutrient-dense produce, and are more likely to have affordable grass-fed meats.
Link disclaimer: a lot of these links are blogs and other such unreliable sources. I don't expect them to be enough to convince you to start avoiding grains; I've simply tried to include an overview of what I've been learning through my own research, and these people have done a better job of pulling the information together than I can (or want to) do. I think only one is a direct link to a scientific study. Still, if you care about your long-term health, I encourage you to do your own research. As for an overview on the evolutionary aspect of eating grains, check out these posts by neurobiologist Dr. Stephan Guyanet.