Sandwiches and burgers were the only broad food category to post growth at both quick-service restaurants and full-service restaurants last year, according to The NPD Group. In a year when restaurant traffic experienced consecutive quarterly declines, NPD foodservice market research found that U.S. restaurant consumers consumed more than 22 billion sandwiches, burgers, and wraps.

"The reason for this growth is this category is one of the few that has mass appeal," said Bonnie Riggs, NPD's restaurant industry analyst. "Sandwiches, burgers and wraps are accessible, customizable, affordable, and portable, and theycan be dressed up, gourmet-style, or dressed down."

According to NPD, total servings of deli and wrap sandwich servings totaled 12 billion in 2009, an increase of 1 billion servings since 2005. Total servings of burgers in 2009 reached 9.3 billion, an increase of 800,000 servings since 2005.

And while all dayparts contributed to sandwich gains last year, lunch contributed to 48 percent of the growth.