While Americans try to find money to plow into retirement accounts and 401(k) plans, most seem to be neglecting another crucial savings account -- the all-important rainy day fund.

"One of the biggest mistakes people make is the failure to create an emergency fund," said Divam Mehta, founder of Mehta Financial Group in Virginia. "An emergency fund is the single most critical component of an individual's or families financial plan."

While it may be crucial, it is not reality for most, according to a new survey by GOBankingRates.com. Nearly 70% of Americans have less than $1,000 in their savings account -- and in fact, 34% say they have no savings at all.

"An emergency fund, especially in this transitory period where there is uncertainty in the market, can become the difference between financial survival and an unclimbable mountain of debt," Mehta said. "As such, without an emergency fund, people are often left to rack up credit card debt when there is an unexpected occurrences."

Mehta said he emphasizes with clients that an emergency fund should be six months of fixed costs -- insurance, groceries, rent/mortgage, etc. While it may take time to build this emergency fund, many people fail to install this major step during their budgeting and financial plan. To address that, Mehta suggests clients make small automated monthly contributions to either a savings account or money market account to build the emergency fund.

Laurie Samay, a certified financial planner with Palisades Hudson Financial Group in Scarsdale, N.Y., said six months of living expenses is a good rule of thumb since it should give enough to fall back on if someone loses their job, decides to leave a job or experiences a health emergency.

"If you are older and/or have dependents, an emergency fund covering 12 months of expenses may be more appropriate," Samay said. "Your emergency fund will give you the opportunity to get back on your feet without turning to debt."

According to the survey, many Americans go without an emergency fund just for the simple reasons of living beyond their means and not keeping to a budget. However, saving for a rainy day can be easy.

Samay said depending on the minimums and fees at one's bank, it may make sense to set up a separate account for an emergency fund and auto-transfer contributions to it each month until the fund's goal has been met.

"This way, you don't accidentally tap into the funds before an emergency transpires," she said.

Once someone hits the six-month target, it's can be a good idea to continue saving from each paycheck, but instead of putting that money into a savings account, you can invest it, said Ryan Kwiatkowski with Retirement Solutions.

"Once liquidity starts to overflow on that six month number, start to put some of it to work in the market," he said. "Have to take some out for a financial emergency? Begin to rebuild it from current cash flow and always have it in case of the next future emergency."

One also could invest their emergency fund, said Samay, as long as you do it carefully.

"As far as how to invest your emergency fund, I'd recommend you consider conservative and highly liquid investments with short maturities and little to no redemption fees," Samay said. "With these types of investments, you will be able to access the money on short notice, which is usually the case with emergencies. I'd also recommend that you keep a portion in cash or money market funds."

Perhaps the most important thing to remember about emergency funds is that they are just that — for an emergency.

"I emphasize with people not to treat this account as something they can dip into for vacations or big-ticket expenses," Mehta said. "Remaining disciplined with building an emergency fund is critical to overall financial success."