When creating your portfolio, you don't need to hold an equal amount of each stock in order to diversify. For the stocks that are the most promising and the best of the best, it makes sense to build your portfolio around them. Warren Buffett's Berkshire Hathaway (NYSE: BRK.A)(NYSE: BRK.B) deploys that approach, and Apple makes up more than 44% of the company's overall portfolio.

Berkshire's strategy over the years has been simply to buy and hold. While there has sometimes been quite a bit of turnover in its holdings from one year to the next, generally the top holdings have remained intact, acting as pillars.

Berkshire released its annual report last month, which featured Buffett's letter to shareholders. The billionaire investor used the letter to highlight a couple of companies that have been key to its business and that are a part of its "secret sauce" -- Coca-Cola (KO 0.30%) and American Express (AXP -0.82%).

1. Coca-Cola

In 1994, Berkshire finished buying shares of Coca-Cola, one of Buffett's favorite investments. Today, the beverage company is one of the top holdings in its portfolio, at more than 7% of its value. It's a business that Buffett is fond of in large part due to its strong brand and the moat, or competitive advantage, that it enjoys.

That advantage is evident in Coca-Cola's most recent earnings report, which featured revenue totaling $43 billion for 2022, an 11% increase year over year. The company was able to raise prices to offset inflation, enabling it to boost its sales and protect its margins -- its comparable adjusted earnings per share (EPS) rose by 7%.

Coca-Cola wouldn't be able to do that if it didn't benefit from having a strong brand, and products that would be in demand even as its prices rose.

Another reason Buffett loves the stock is its dividend. In February, the company announced that for the 61st straight year, the dividend will be going up.

Coca-Cola is a Dividend King and among the best dividend growth stocks you can find. Buffett notes in his shareholder letter that Berkshire earned $75 million in dividends in 1994 and $704 million this past year. And he believes it's "highly likely" that those payments will continue to grow.

For long-term investors, Coca-Cola is also a great business since it's fairly low risk, profitable, stable, and offers a great dividend that today yields just over 3%.

2. American Express

Another company that Buffett includes in his secret sauce is American Express. The credit card company's business is resilient, like Coca-Cola's. Whether consumers are doing well or are struggling, they'll often use their credit card to make purchases, if for no other reason than to accumulate points.

American Express also targets a more affluent customer, which can make it a safer investment amid inflation. The company said in its recent earnings report that "our credit metrics remain strong, supported by our premium customer base."

Amex is coming off a strong year in 2022, when revenue net of interest expense totaled $52.9 billion and rose an impressive 25% year over year. Rising costs did chip away at earnings, but diluted EPS of $9.85 was down just 2% from the previous year. For 2023, the company is expecting its revenue to grow between 15% and 17%, and for EPS to come within a range of $11 and $11.40.

Berkshire "essentially completed" its investment in American Express in 1995, which also makes up 7% of its portfolio today. And while it doesn't have the streak going that Coca-Cola does, Berkshire has seen its dividend income soar over the years from this investment as well, from $41 million to $302 million.

The company paused its increases during the early stages of the pandemic but now has resumed them. Earlier this month, the board of directors approved a quarterly dividend of $0.60, which is a 15% increase.

At 1.5%, American Express offers a decent dividend yield to go along with all that growth the business is experiencing. For investors, this is another great investment to hold for the long term.