Planning for a financially secure retirement may seem like an impossible task, but it's not. With the right investments in your portfolio, you can reach goals you might have thought were out of your reach. The key, though, is making sure you have all your bases covered with a coherent, sensible plan.

The danger of haphazard planning
All too often, people's portfolios end up looking like the financial equivalent of a teenager's bedroom. See if this looks familiar to you: Many people end up with a hodgepodge of different stocks and funds picked up at various times and then forgotten about. And for those fortunate enough to have a 401(k) or similar employer-sponsored retirement plan at work, plenty of folks simply pick a single investment option and let things roll on autopilot for years without any attention.

Obviously, that's not the right way to plan for retirement. Using a simple asset allocation strategy is the best way to build a diversified portfolio that will build your wealth throughout your career. But there are some key components that many people leave out of their asset allocations, and without them, you could be putting your financial health at risk. Let's talk about three of those key elements of a successful plan.

1. Own international investments.
For a long time, financial professionals recommended that investors keep most of their money close to home. With political turmoil around the world and a lack of information, investing in little-known foreign stocks involved quite a bit of risk.

But now, times have changed. The global economy has made it not only possible but essential to keep your finger on the pulse of worldwide news and business conditions. Moreover, with the rise of foreign economies, keeping all your eggs in the U.S. basket is risky -- as the fall of the dollar in recent years has reminded investors.

Fortunately, ETFs have made international investing simple. Vanguard Total International ETF (Nasdaq: VXUS) provides balanced exposure to both developed and emerging markets around the world. If you prefer to focus only on the faster-growing emerging economies, iShares MSCI Emerging Markets (NYSE: EEM) owns many big stocks in countries including Brazil, China, and India. Either way, going beyond your borders can enhance your returns.

2. Keep it real.
Many companies thrive by taking raw materials and creating products that add significant value. But as some of the world's biggest countries grow more prosperous, demand for those raw materials may well supplant the value added later in the production process.

We've certainly seen that trend play out in recent years. Despite plenty of bumps along the way, oil and gasoline prices remain at high levels. Shareholders in rare-earth metal play Molycorp (NYSE: MCP) have profited handsomely as concerns about supplies of strategically important metals have led to international trade restrictions and raised national security issues. From Suncor's (NYSE: SU) big investments in oil sands to unconventional oil and gas plays throughout the world, the race to secure natural resources has heated up.

Increasingly, you have several options to invest in this trend. Mining and energy stocks are the longtime favorite, but ETFs like Sprott Physical Gold Trust now exist whose sole purpose is to hold raw commodities. Both methods have their advantages and disadvantages, but no matter how you get it, some type of exposure to the vital inputs to economic production is essential.

3. Get some income.
Historically, investors haven't worried about income until they've actually reached retirement and need the money. But now, you need to plan for the contingency of having to draw income from your investments before you reach retirement age.

That's where income investments come in. Bonds and bank CDs are traditional ways to avoid the risk of stocks, but their rates are at rock-bottom levels right now. Meanwhile, several blue-chip stocks have very attractive yields at current prices. Combined with more exotic investments including real-estate investment trusts and master limited partnerships, it's easy to generate the dividend income you need to supplement your cash flow. With REIT Chimera Investment (NYSE: CIM) yielding well over 10% and MLP Cheniere Energy Partners (AMEX: CQP) pushing the 10% mark, there's no shortage of reasonable -- though definitely not risk-free -- choices for you to consider.

Don't miss out
A comfortable retirement may seem out of reach given today's economic challenges. But don't give up. By making sure your investment portfolio includes these three types of investments, you'll improve your chances of having the retirement you've always dreamed of.

If you're trying to retire rich, you need to know the basics. Our 13 Steps to Investing Foolishly will get you on track to a great financial plan in no time.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.