Following some simple things while shopping gives you more options, and a healthier meal.
1. Always read labels to compare products. For example, compare total calories on same salad dressings of different brands -- and then go for the one that has the least number of calories.
2. Keep a well-stocked kitchen at all times, so that you don't eat high-calorie food for lack of better options.
3. Stock-up on some basic products like low-fat cheese, skim milk, yogurt, and eggs.
4. Fresh fruits are always a better option. But you can also go for fresh, frozen fruits in light syrup.
5. While buying vegetables, go for ones that are plain frozen rather than mixed with butter sauce.
6. Go for low-fat cereals, pita bread, and diet margarine.
7. While buying fish, avoid ones that are already battered.
8. Finally, avoid food that is highly processed.
I really like your point #2 ... it's something that happens so often to many people but aren't aware of it. Many folks will consciously admit they shouldn't be eating that bag of cheetos, but usually rationalize it as not having anything else. As for #6, there is also a butter substitute made of soy, I think.. I personally couldn't tell the difference.
Think like Alice Waters and other professional chefs: think local, seasonal and fresh. This means, check out your produce section when you get there...things may look appealing that you never thought of. Things on a list may look squished or bruised or shriveled. Keep a nice pantry of a variety of beans and rice -- just like rock star Andy Tanas does. Try beans and peas that you may never have eaten, like Black Eyed Peas. They store forever, really.
Herbs should be fresh. All those spice mixes and jarred garlic are disgusting.
Use a fresh pepper mill for fresher taste. Try different salts from around the world -- some are so flavorful, you only have to use a little.
Keep high quality cocoas and teas around, as well as stocks. These can all flavor sauces easily.
I like having a good quality cheese grater, for fresher, non waxy grated cheese.
Bags of frozen fruit are appealing in the winter for a quick dessert.
Whole grain and spinach pastas are easy to dress up.
You WILL appreciate having fancy olive oils and vinegars in the house, for your own dressings. If you have a hand immersion blender (check out HSN.com), then your dressings will look like a chef made them.
I also like having high quality extracts, such as Bourbon vanilla, to flavor yogurt or puddings and sweeten with Splenda.
These are all great tips. I'm with Tamar, I like to make and season my own food as much as possible. I keep a good selection of seasonings and oils on hand.
As far as eating foods that aren't healty, I find that if they aren't in the house I don't tend to eat them. If you do buy chips for a snack or a meal. Stick to the small three serving size bag or get the little ones that cost a quarter. Sometimes when I make chili I want a Frito pie. If I get the little bags then I only eat a serving. If I buy the big package. Watch out!