Skip the Unicorn Frappuccino and other tips for millennials who want to retire well

  • Millennials can't wait till later to start preparing for retirement.
  • Here are 5 steps millennials can take now to boost their nest eggs.

Millennials need to think of themselves as Generation Invest.

These young Americans are often portrayed as having short attention spans and being unable to stay focused on anything longer than a Snapchat video. While this may be an unfair characterization for most, there's one area in life where millennials absolutely cannot afford to live up to this stereotype - planning for retirement.

This generation is living longer: Millennial men and women have a 27.3 percent and a 39.5 percent chance, respectively, of seeing their 90th birthdays. But with the uncertain future of entitlement programs like Social Security, it's crucial for Gen Y to start planning their financial futures and take advantage of all the time they have now to accommodate a long life ahead.

Here are five things millennials can start doing now to ensure they'll have enough money to live comfortably in their golden years.

1. Start investing, now

Millennials have a lot on their plates. Student loans, credit card debt and a higher cost of living make it easy to give up early on the idea of investing for the future. Luckily, there are numerous investment apps available to all consumers regardless of wallet size. All millennials need to do is commit to starting small and growing from there.

Time is money and millennials have a lot of time on their side to start building toward their future. The key is to start early and allocate however much money you feel comfortable setting aside for investing.

It isn't easy putting off instant gratification to save for a far-away date. But simply getting into the habit of investing and seeing one's portfolio accumulate more wealth as time goes on is a rewarding and empowering feeling.

2. Take advantage of employer-sponsored retirement plans

Employee benefits may be hard to understand but it's worth it to take the time and understand the offerings. Maximizing the benefits of an employer sponsored retirement account such as a 401(k) or a 403 (b) is one of the best and easiest financial habits a young professional can develop.

Millennials should understand the matching principals of these plans and start contributing even if it's just a small percentage at first. They needn't feel pressure to put too much in at first they can always adjust that percentage after every pay raise.

Often, millennials will opt-out of these plans early in their careers because they believe they need that money available to them. This is proof that they're not getting the education they need to see the longer-term benefits of compounding interest. Fewer than half of millennials - 48 percent - contribute to a 401(k) plan, according to a recent survey Stash conducted on American financial literacy. Not taking advantage of an employer-match is basically throwing free money out the window and no one wants to do that.

3. Develop a side hustle

We get it, life in the 21st century as a millennial is anything but cheap. Entire paychecks are allocated to food, rent and life's necessities. What our parents called getting a second job, millennials call a creative side-hustle. No matter what you call it or what it is, it can make a huge difference in your future finances.

A side-hustle can help millennials make that extra income they need to free up more money in their take-home salaries to be contributed to a retirement account or other investments like saving for a home. Plus, side-hustles most often closely align with people's passions. Whether that's teaching a meet-up group a new skill, freelance writing or taking-up a part-time bartending gig, side-hustles can alleviate anxiety about saving money for retirement while being a change of pace from regular work life.

4. Dust off that old piggy bank

Remember as a child how you would put spare change in a piggy bank and at the end of the year take your change to the bank and come home with a stack of cash? Your piggy bank may be gathering dust in your parents' basement but the lesson is still there.

It's a put it on the plastic world but when you use cash, take the change and immediately drop it into your piggy bank (or whatever your modern version of a piggy bank is). Whether that's leftover money from a dinner or from the laundromat, stash it away and forget about it. At the end of the year, add up all this spare change and put a chunk of it into your savings account to accumulate interest.

Suppose you put $10 in leftover change into your piggy bank a week. At the end of the year that's $120 in savings towards your retirement that would have been wasted on indulgences. Start doing this at age 21 until retirement - say for 44 years - you will have saved approximately $5,280. Call me crazy, but that could make for some great shuffleboard money in your later years

5. Reallocate funds

A $6 Unicorn Frappuccino? It may be tasty now but after the last drop is gone, so is the chance of making that money grow. Believe it or not, skipping one high-priced coffee a month and reallocating that money into an investment portfolio can help millennials in the long-run. Little indulgences add-up, especially if they are done everyday. Millennials should see where they can cut back without it negatively impacting their quality of life.

There are a lot of options for millennials to save for their retirement goals and begin building smart financial habits. No one expects them to save like their parents did, nor should they. It's totally different world from theirs. But when it comes to saving and investing money, the earlier one starts, the faster these habits will become routine and before millennials know it, they'll be coasting into retirement with a nice nest egg and a lot less worry.

Commentary by Brandon Krieg, co-founder and CEO of Stash, a mobile investing platform. Follow him on Twitter @brandonkrieg1.

Follow CNBC's Opinion section on Twitter @CNBCopinion.

Watch: How millennials should prepare for retirement