Most (82 percent) millennials believe society will eventually become cashless, even though they're the generation most likely to favor cash when traveling, according to a TD Bank Consumer Spending Index. 

What's more, if their cashless payment method of the future is a credit card, that could be a problem, because millennials lack healthy credit habits. For instance, the study found that among millennials who use credit cards: 

• Half use 31–90 percent of their credit limit, surpassing the recommended rate of 30 percent or less.
• 32 percent don't pay their cards off in full each month, which is costly and can damage credit health.
• Despite being more likely than other generations to pay for a group outing in order to earn rewards, 30 percent of millennials have let their credit card rewards expire, compared with 14 percent of Gen X-ers and 9 percent of boomers. 
• A quarter of millennials do not know their credit score. 

"The data is a bit concerning," Mike Kinane, head of U.S. bankcard at TD Bank, said in a press release. "We're relying less and less on cash, and while credit cards may not be a millennial's payment method of choice, it's still critical that they develop financial knowledge and habits to properly position themselves for sound credit health down the road."