Credit unions shouldn't assume that will be the case in the 2019 holiday shopping season, however.

"I hope that credit unions don't get extremely excited about the lift," Patrick said. "I think we ended the year on a fantastic note, but I think some economic conditions that are lining up may not paint as rosy of a picture as we look forward."

2. Fraud Detection Systems Must be Ready by Thanksgiving

The holiday shopping season is one of the busiest times of year for criminal activity, according to new data, and the 2019 holiday shopping season starts just nine months from now. Identity security firm Jumio, for example, reported in December that online fraud attempts on government-issued IDs spiked 22% between Black Friday and Cyber Monday in 2018. Fraud attempts involving passports, driver's licenses or ID cards hit a five-year high, up 109% from 2014.

On top of that, in January electronic payments firm ACI Worldwide reported a 13% rise in fraud attempts that involved "buy online, pickup in-store" transactions during the 2018 holiday season.

"As chip-and-pin credit cards are harder for fraudsters to replicate, it is driving them toward card-not-present, cross-channel fraud," ACI Worldwide Global Director of Payments Risk Erika Dietrich said. "For example, fraudsters can use stolen credit card information to make a card-not-present purchase online and then simply walk in and pick up the item in-store. We'll see this trend continue to grow in the coming years, and merchants will need to pay more attention to their omnichannel fraud controls."

3. Address the Competition for Wallet Space Now

Consumers used twice as many cards for their spending during the 2018 holiday season compared to 2017's organic growth, PSCU noted. "PSCU owner credit unions saw between 4% and 5% organic card growth, but up to 9% growth in total cards that were actually spending over the holiday season," the CUSO reported.

"There is a significant amount of competition out there coming from every direction possible. The fact that credit unions were able to double over their organic growth, given the competitive environment – that's a heck of a story for credit unions," PSCU SVP and Chief Marketing Officer Tom Pierce said.

The jump in the total number of cards in use opens some doors today for credit unions, according to PSCU Vice President of Analytics Strategy and Engagement Jeff Rosenbeck.

"There is an opportunity for credit unions to capitalize on the additional cards now in rotation to ensure members continue spending on their credit union card in 2019, and ultimately move that card to the coveted top-of-wallet position," he said.

4. It Isn't All About Credit Cards

The 12% spike in debit card spend during the 2018 holiday season is a big reminder that credit unions shouldn't focus all of their portfolio-development attention on credit cards – especially if the economy softens and it becomes harder to get a credit card or bigger credit line, which could shift more spending to debit cards, Pierce said.

"Credit unions are lenders just like banks are. And when you are a lending shop, you are laser focused on your lending product, such as credit cards," Patrick added. "As we saw with these results through the holiday season, debit was a pretty important cog of growth during the holidays. I think credit unions have a huge opportunity to focus on debit cards, getting not only cards into members' hands, but also getting them to use them more and maximizing the profitability and positioning of the programs overall. I think there's a huge opportunity for focus there."

5. Rewards Programs Are Key

Debit rewards are coming back, according to a recent study by CO-OP Financial Services. Although only 35% of credit union debit card issuers in that survey had debit card rewards programs, another 25% were thinking about adding one. About a quarter said they were reevaluating their rewards or thinking about changing the benefits in their rewards programs, according to CO-OP.

Credit unions should assess and optimize their rewards programs in time for the coming holiday season, Pierce said.

"I think the credit union has a really big responsibility of setting the table as you move forward," he said. "Optimizing the product, optimizing the pricing, the reward structure – it's a continual process and it needs to be continually measured. Credit unions need to continue to do that and really get themselves set up for next year. So, if they do that, [there's] probably a pretty good shot that we'll see great success again next year."

6. How Members Paid Last Year Could Be Wildly Different This Year

Contactless cards, which transmit payment transaction data when they are within a few inches of an enabled point-of-sale terminal, are growing rapidly. According to data from the U.S. Payments Forum, more than 50% of transactions now take place at merchants that have enabled contactless payments. The organization also predicted that more merchants will become able to accept the dual-interface cards expected to hit the market in 2019.

That could leave many credit unions with just a few short months to figure out where their payments portfolios fit.

"As we look at next holiday season, the other factor that's going to start to play in the mix in 2019 is: How are credit unions potentially shifting to a contactless card?" Pierce asked.

"Globally, I know as the contactless cards have been introduced, it hasn't been as much a shift from debit. It's been a shift from cash into that. So, that could be a transaction growth opportunity for credit unions for next year and this coming holiday season," he added.