This year is proving to be an unpredictable one for the markets; 2020 has featured some of the largest single-day declines investors have seen in decades, and the S&P 500 has also hit new all-time highs. That instability makes it a good idea to prepare now for a market crash, because it could happen again -- this year.

You can protect your portfolio and minimize the impact of a crash by investing in blue-chip stocks with strong business models that are trading at modest valuations. GlaxoSmithKline (NYSE:GSK)Coca-Cola (NYSE:KO), and Verizon (NYSE:VZ) are all examples of investments you can safely hang on to right now, even if we see another steep decline. And together, they can make your portfolio stronger through diversification. Here's why each stock is a good buy today.

1. GlaxoSmithKline

Healthcare is a solid industry to invest in if you're looking for stability and are worried about a crash. Top drugmaker GlaxoSmithKline makes a variety of drugs to serve many different patients, and its diverse portfolio of products makes it a stable buy. Its major pharmaceutical segments include respiratory, HIV, immuno-inflammation, and oncology, and its focus on innovation is what makes it so exciting. Currently, the U.K.-based company is working on 35 medicines in its pipeline and 15 vaccines.

Red arrow going down with dollar bill in the background.

Image source: Getty Images.

And with GlaxoSmithKline branching off into two different companies -- one that's focused primarily on research and development and a new one that will focus on consumer healthcare -- the move should help drive even more new products to market in the coming years. Management is also currently working with Sanofi to develop a vaccine for COVID-19. The two agreed to a deal in July to supply the U.K. government with up to 60 million doses of their vaccine.

GlaxoSmithKline has reported a profit in each of the past five years, and during that time its revenue has grown by 41.1%, reaching 33.8 billion pounds in 2019. In the company's second-quarter results, released July 29 for the period ending June 30, sales remained strong despite the effects of COVID-19 -- its total of 7.6 billion pounds was down by just 2% year over year.

Today, the stock trades at less than 12 times its earnings, a bit cheaper than its P/E over the past few years. It is an attractive buy for value investors.

2. Coca-Cola

It's hard to go wrong with a top Warren Buffett stock like Coca-Cola when picking solid investments that can survive some tough times ahead. The beverage company owns dozens of popular beverage brands, and it has evolved over the years to offer healthy products for consumers in addition to its sweeter drinks.

Although sales growth may be hard to come by, which is understandable for a company as big as Coca-Cola, its financials remain strong, with operating income consistently falling between $8 billion and $11 billion in each of the past 10 years. Strong gross margins of at least 60% also make it easy for the company to cover its operating expenses, which rarely come in higher than 40% of revenue.

Business shutdowns and lockdowns weighed on the company's most recent results, released July 21, with Coca-Cola reporting net revenue of $7.2 billion for the period ending June 26, down 28% year over year. Its earnings per share of $0.41 were also down 32% from the prior-year period. But with more cities reopening, the third quarter should prove to be a better one when the company releases its updated results later this year.

Coca-Cola is still an industry leader after all its years of dominance, and that appears unlikely to change anytime soon. Its shares currently trade at 22 times earnings after spending most of 2019 with a P/E near 30 -- and that's after a bad quarter. With a modest valuation and a business that's still showing no signs of straying from the black, this is one stock you likely won't have to worry about falling heavily in value during a market crash.

3. Verizon

Telecom giant Verizon is a cheap, stable buy that could also offer investors some attractive growth opportunities. It provides essential internet services to nearly 120 million Americans every day, whether on their mobile phones or inside their homes. And as it continues to build out its 5G network across the country, it will create future growth opportunities in the form of new service plans as consumers take advantage of faster internet speeds -- so far, its new 5G plans are only available in select markets.

Verizon's financials are pretty consistent, with a profit margin of at least 10% in each of its past five years. There hasn't been much volatility in its revenue over that time, either, with sales falling within a range of $125 billion to $132 billion. And it's still proving to be stable amid COVID-19. In second-quarter results, released July 24 for the period ending June 30, Verizon's sales of $30.4 billion were down a modest 5.1%. The decline -- which took place during a coronavirus-affected quarter -- was still better than the $29.9 billion analysts were expecting.

Today, the stock is trading at a very reasonable 13 times its earnings. 

Which stock is the best buy?

All three of these stocks are solid buys, but which one is the best? Here's how they're doing so far this year:

GSK Chart

GSK data by YCharts

The S&P 500 has outperformed all three stocks on this list, and that's probably no surprise -- they're all cheap stocks that investors haven't been buying up this year. Of these, the stock I'd go with today is GlaxoSmithKline. Although its price has fallen the most this year, it has many products in its pipeline along with the work it's doing on a vaccine, all positive developments that could lead to significant growth down the road.

However, it's hard to go wrong with any stock on this list, as they are all well positioned to survive a crash and do better than other high-priced stocks in the markets today. 

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.