Snacking -- once viewed as a vice -- has evolved into a virtue, as consumers seek a burst of energy throughout the day with protein-packed bars, tubs of yogurt or other convenient items.

Snacking had a "bad rap as the thing you do in the whim of the moment," said Amy Martin, a strategic planner with Saatchi & Saatchi. But now it is more "purposeful," she said, as parents realize that "snacks are accounting for more of the nutritional intake of their families and their kids."

Snacks account for a third of the calories consumed daily by adults, according to a Rabobank Group report. The typical U.S. consumer snacks two to three times a day, and "many have gone a step further" with snacking becoming the "default way of eating" rather than the standard three meals a day, finds the report, called "Never Eat More Than You Can Lift."

The clear winners are snack bars, whose market size has more than doubled in the past 10 years to $6 billion, outpacing chips and pretzels, which grew 3.5% to $34 billion. The report cites Clif Bar & Co. as a growth leader thanks to its "socially conscious credentials" and "hip image." Meanwhile, General Mills U.S. snacks division -- which includes Nature Valley and Fiber One bars -- grew 15% in sales in fiscal 2012 and accounts for 9% of company sales, leaving it only a couple percentage points shy of its Pillsbury unit, according to a report by Bernstein Research.