It’s the most wonderful time of the year! While you’re enjoying the festivities that the holiday season brings, now may be a great time to start thinking about how you’re planning to put your 2018 TFSA contributions to work. If you’ve got enough cash on the sidelines, you might want to ring in the new year by making a full contribution to unlock the full power of compounding.

What should you be putting in your TFSA? If you’re a young investor with a long-term time horizon, your best bet would be to own high-quality stocks with top-tier growth profiles to grow your TFSA at the quickest rate. If you’re a retiree or an older investor who’s planning to retire soon, it may be worthwhile to own defensive income names to preserve the wealth in your TFSA that you’ve worked hard to amass over the years.

This piece will be geared towards younger investors who are at least 10 years away from retirement. So, without further ado, here are two undervalued growth names you should think about buying with your TFSA contribution for 2018.

Restaurant Brands International Inc. (TSX:QSR)(NYSE:QSR)

Restaurant Brands is my largest Canadian holding, and I intend to hang on to shares for decades. Many investors have been turned off by the stock because of its high debt load, but I think that’s a mistake given the company’s potential to accelerate free cash flow over the next few years.

Shares may seem expensive, but I believe they’re actually a great value at current levels when you consider you’re getting an incredible management team in 3G Capital — a king when it comes to operational efficiency. In addition, the sky’s the limit when it comes to growth potential since, as the name suggests, more acquisitions are likely to happen over the next few years, all while management continues to expand and drive comps with its existing brands.

Shares recently took a tumble following a barrage of short-term developments, none of which are detrimental to the company’s fundamentals.

Alimentation Couche Tard Inc. (TSX:ATD.B)

Couche Tard is an earnings-growth superstar and a king of M&A, but more recently, the stock has gone into hibernation, as fellow Fool contributor Will Ashworth pointed out.

The pace of acquisitions has slowed, and debt levels have increased significantly over the past year, but in the longer-term picture, I don’t think this is a reason for investors to throw in the towel, especially since the recent acquisition of CST Brands is its largest to date, and there are still plenty of synergy opportunities that have yet to be realized. Over the next few years, synergies will be realized from recent acquisitions, and this will support earnings growth of ~20% over the next few years.

In addition, Couche Tard may begin an expansion into select Asian markets, which could support CAGR in the high double digits. And looking into the longer term, Couche Tard may end up selling cannabis at its stores once regulators become more open to alternative non-traditional means of sales.

Stay hungry. Stay Foolish.