"They expect to have a relationship with the brands they support because their lives are so visible," Gutfreund said. "Everyone knows what everyone else is doing. They also believe that shopping is a new activism. If they're going to buy something, it's a vote. They believe they are investing in a brand and expect the same level of recognition and acknowledgment a company would give to a shareholders."

Often, young consumers want to customize and personalize their products, prompting some retailers to revamp logos to play down the brand, a step taken by Aeorpostale, and others to dream up new concepts, such as Nike's new store concept Salvation, where consumers can design their own image for their Nike and Converse footwear.

Gen Y's desire for instant gratification hasn't been lost on retailers, as online behemoth Amazon.com builds more warehouses to increase same-day shipping, retailers encourage shoppers to place online orders on in-store computers to prevent them from feeling they've left empty-handed and online sellers allow in-store pickup and returns.

"This is a generation that has been, I don't want to say coddled, but had great attention paid to it by parents and doting aunts and uncles," McAvey said "The thought that they would order something and not be sure that they really like it and wait a week for it to come is not as appealing to them."

Katie Furtado, 28, who was shopping with her 2-year-old-daughter, Sophie, at Target in Aberdeen, described herself as just that type of consumer. The desire to get the stuff she wants and needs fast keeps her mostly offline.

"I never shop online. I have no patience," said Furtado, Besides, added the stay-at-home mom and business administration student, "I can't stand having to pay for shipping when I can drive a few miles. I'd rather get out of my house."

Her husband once ordered diapers online, but she got tired of waiting for delivery and went to the store herself.

Gutfreund expects retailers to cater more and more to Gen Y. Many will integrate their online and physical channels to give consumers a more seamless experience, such as Nordstrom, which highlights items in stores that are featured on photo-sharing website Pinterest, and Lululemon, which offers an app that directs customers to an area's yoga classes.

She also expects retailers will make greater use of data to customize consumer marketing and place greater emphasis on service as consumers rely more heavily on online reviews.

Retailers are keeping a close eye on the millennials' buying habits because it's becoming clear that they are not just a younger version of their elders, but a different shopper altogether, McAvey said.

"Many people speculate this is going to be the sharing generation," more apt to rent a zip car or ride a bicycle than buy a car or use a tie-sharing service rather than having a closet full of the accessory, she said. "It's not clear that they wish to acquire as much stuff as their parents did, and retailers are very interested in what they're going to do."