The same study he references also pointed out that in 1960 Americans spent 17.5% of income on food, and 5% on health care. Now we spend 10% on food and 16% on health care--this flip-flop shouldn't be so shocking, but it is!
Given these health considerations, buying the cheapest of everything is not my highest priority. However, it IS important to me that I get a good price on whatever I do buy, and also that I avoid wasting money. Here are the strategies I try to use:
1) Plan meals in advance. Try to sit down once a week and plan out the meals you will prepare every day. Don't forget to factor in leftovers too, of course. As a single, I find that the typical recipe usually lasts me for 2 dinners and 1 lunch (with additional sides).
2) Have a shopping list. Since you'll have planned meals in advance, you'll need this anyway. A shopping list makes sure you get everything you need, avoiding frustrated take-out orders when you discover you're out of butter. It also prevents you from wandering and picking up random items that are bound to be either wasted or unhealthy. Supermarkets are designed to take advantage of aimless shoppers--don't be one of them!
3) Try to shop daily, every other day, or as close to it as possible. Make it a habit to stop at the grocery store or market once a day, maybe on your way home from work. Since you'll be buying for just one or two meals, your stops will be quick. This tactic is healthier, since you'll be eating everything fresh, and it's cheaper, since you won't be buying things you "might" want to eat later in the week.
4) Find your neighborhood farmers' market!! They're all over the place these days, selling locally grown (i.e. fresher) produce for good prices. Greenmarkets in the city are generally pretty good--find one by neighborhood at this link, with directions and descriptions included. If that doesn't work, check out this general listing of farmers' markets here.
---My favorite farmers' market is the Stiles Farmers' Market in Manhattan. There are two locations--the one on 52nd Street between 8th and 9th avenues (link goes to its Yelp page) is far superior, but the location on 9th avenue between 41st and 42nd streets is also excellent. Produce is fresh and local (not organic), so they only sell what's in season. The prices are just incredible (you'll cry at all the money you wasted at Whole Foods!).
---Fairway is also a good bet for cheap and yummy produce.
5) Cut back on your meat consumption! This is the single most important move you can make for a lot of reasons: to decrease your negative impact on the environment, to encourage moderation in the meat industry, or to improve your own health— but it also will do tons to lower your grocery bill. Beans, grains and vegetables are all crazy cheap, so fill up on them! Head over to the New York Public Library and check out How to Cook Everything Vegetarian by Mark Bittman for simple recipes.
--Bonus: If you focus on vegetables that are in season, you'll also save loads. Anything that has to be shipped from another climate will have those transportation costs factored into the price (think: oil). Here's a great resource on figuring out what veggies are in season.