Low gas prices may have left extra cash in car owners' pockets this year, but chances are it's not staying there. When asked what they were doing with any extra money, 40 percent of Americans said they used it to pay for other necessities such as groceries and rent, according to a survey that accompanied Bankrate's Financial Security Index for May. Another 14 percent of survey participants said their savings went to nonessentials like dining out or taking a vacation. "In a testament to tight household budgets, more Americans spent the savings from lower gasoline prices on necessities than anything else," says Greg McBride, CFA, Bankrate's chief financial analyst. Gas prices have fallen 28 percent over the past 12 months, according to a Bankrate analysis of government data.