It's a beautiful, terrifying day when your children start feeding themselves. Not the hold-his-own-utensil, pincher-grasp-her-own-banana feeding. That's unadulterated beauty. The terrifying part arrives when your kid is old enough to hop in the car, drive to the store and buy his or her own "food." Will a vegetable make its way into the cart? Will expiration dates be checked? Will Cool Ranch Doritos and Red Bull rule the day? Hard to say. All you can do is arm your young shopper with the knowledge to navigate a grocery store in a healthful, budget-conscious way. Registered dietitian Jill Castle is here to help. "Your main goal with teens is pushing them toward variety and helping them identify health-promoting foods," said Castle, co-author of "Fearless Feeding: How to Raise Healthy Eaters From High Chair to High School" (Jossey-Bass/Wiley, $16.95). In that spirit, she recommends imparting the following wisdom:

Eyeball ingredients

"I advise teens to look at the first three ingredients," Castle said. "You want to be able to identify what's in it, and you want to be able to pronounce it. If you look at a bag of Lay's potato chips, the ingredients are potatoes, salt, oil. If you pick up a bag of cheesy Doritos, you see a lot of chemicals you can't pronounce."

Pay attention to portion

Make sure your teen knows where to find the serving size on nutrition labels and point out that some items, particularly less healthy foods, are packaged to be wiped out in one sitting — but, nutritionally, shouldn't be.

"Show them, 'This is a normal portion,' and 'This 24-ounce soda is more than twice a single portion,' " she said.

Browse the aisles

"Shop the perimeter" is a grocery shopping mantra — logic being that produce, dairy and less processed, packaged choices dwell along the outer limits. Castle encourages teens to venture into the inner aisles in search of whole grains and nonperishables.

"Nuts and seeds and dried fruits, healthier oils, beans, whole grain pastas, brown rice — there are lots of good finds in the aisles," she said.

Pick produce wisely

"Look for fragrance, firmness and color" when choosing fruits and veggies, she said. And think twice before going the convenience route: Bagged lettuce, baby carrots and sliced apples are time savers, but they cost more and often are treated with chemicals or other preservatives. And educate your teen on produce shelf life.

"I tell them to always have onions, potatoes and celery on hand," she said. "They're the bases for soups and so many different meals, and they're not quick to perish."

Make dairy count

Point them to the milk, yogurt, butter and cheese and encourage them to get familiar with their calorie counts and fat content.

"I'm not always a fan of sugar-free or nonfat for teens, though," Castle said. "The key to feeding teens is giving them choices that are satisfying in terms of taste and hunger so they're not snacking constantly."