The average person spends $67 a day on discretionary stuff like gas, coffee and takeout food.

But if you keep even just a few of those dollars, it can make a big difference in your net worth.

Now, I won't tell you to skip your daily coffee. I consider my Dunkin (DNKN) runs essential. You're never going to get rich by denying yourself small luxuries.

But do look at your subscriptions. Things like Amazon Prime, Netflix, or a gym membership. You might pay them monthly or annually, but you can get enjoyment from them every day.

The point is, see if you can get your spending to average $67 a day.

Get it even lower, and you'll open yourself up to bigger luxuries … like retirement.

A $40 Spending Cap Now Can Buy a Lot of Freedom Later

If you spend $67 a day, that's about $2,000 a month and a little over $24,000 a year.

If you make $50,000, you're spending almost half your salary on discretionary items.

It's easy to get away from that $67 a day average limit … in the wrong direction. If you know you like to make impulse purchases, for example, you might budget most of that for Amazon (AMZN) and adjust your gas and food lower.

Better yet, budget $40 for gas, food and other items. Then you'll have an extra $27 a day to play around with.

That's $800 a month you can spend on other stuff … or, even better, save.

Spend $50 Today … and Fund Your Retirement for Life

You can keep your coffee and cut out something else. Stop going out to lunch every day. Or buy a more fuel-efficient car and save $2 a day on gas.

Set a goal for yourself. Say you want to save $500 a month. All you have to do is put away $17 a day.

If you can save $500 a month, that's $6,000 a year. And guess what? That's an IRA.

That's right. You can fund your retirement by making lunch at home every day.

If you can save $6,000 a year in your IRA for 40 years, you'll have $240,000. With investment returns, you can easily — conservatively — have $600,000 to $700,000.

That gets you a much better retirement for almost no effort. And you can bank on this hack to get you there.

Jared Dillian writes the free investment newsletter The 10th Man for Mauldin Economics. Subscribe here.