This froma USDA pamphlet that I found on the web. It gives some perspective, but doesn't make the current situation easier. Note that the initial year is 1929, beginning of the Great Depression. Andthe end date is 1997. I don't know what the percent is today.

Food spending has increased considerably over the
years, but the increase has not matched the gain in
disposable income (the amount of money families
and individuals have available to spend or save). As a result, the percentage of income spent for food has
declined. In 1929, the first year data of this
type were recorded, 23.9 percent of disposable
income was spent for food. This percentage has since
tapered off fractionally almost every year. By 1970,
the percentage had dropped to 13.8 percent. During
the 1970��s, the percentage held fairly constant
because of high food-price inflation. By 1980, food
spending was still 13.4 percent of disposable income,
but has since declined steadily to reach a low of 10.7 percent in 1997 .