How did Americans spend their gas savings? We now know

Gas prices went down in 2014. We know that. In fact, the average national gas price in December 2014 was a slim $2.50, down significantly from $3.25 a year prior, in December 2013.

But did that drop in prices lead to fatter wallets, or did Americans spend more on everything else instead?

According to exclusive data provided to CNBC by Cardlytics, a card-linked marketing firm, we now know exactly how those savings were spent. Here's the quick answer:

Fast food and online shopping.

The numbers show that consumers increased their gas consumption by 6 percent, to 33 gallons from 31 gallons for the month on average. Even with that 2-gallon-per-month increase, the cost savings were real, resulting in an extra $18 per month per person. (Quick math shows the product of 31 gallons times $3.25 per gallon is $100.75 per month, much higher than 33 times $2.50, which is only $82.50).

That $18 gas gift didn't stay in Americans' savings accounts, instead it was quickly spent. Cardlytics' data showed that overall spending was up about 2.3 percent, with a heightened 5.3 percent increase just in retail and restaurant categories. That's right, consumers spent more money in total even after spending all of their gas savings. The $18 in gas savings was more than offset by a $45 jump in all other spending, for a total increase of $27.

The biggest winners were e-commerce and eating out. The restaurants that saw the most growth were not the fancy ones though—rather, we saw the highest gains at quick service restaurants (aka fast food). Some categories—health and beauty—fell short of the average 5 percent gain, while sporting goods and office supplies were among the decliners. "Our data shows overall spending is up, consistent with our improving economy," said Kasey Byrne, chief marketing officer for Cardlytics.

Winners
  • Restaurants up 7 percent to $54.39 up from $50.85
  • E-commerce up 10.3 percent, a gain of more than $8 per person
Losers
  • Sporting goods and office supplies saw declines
  • Banquet and catering operations had a drop in sales—but note that this is a very small category within restaurants

A better economy—in addition to the gift of cheap gas—helped increase consumers' confidence, and ability to spend more money. Byrne points out the spending data show a heightened "focus on family," specifically noting consumers "dining out together, spending on home-related items like garden and grocery, even shopping at home with more e-commerce."