Just happened upon this today...
http://www.bundle.com/everybodysmoney
It's an interactive tool that breaks down how people spend their money in every major city. It happens to include monthly spending on groceries at various income levels in each city--as well as shopping, transportation, health, home, etc. The amount of data here is astounding.
They've compiled the food/drink spending into one large chart
here, claiming that Austin is #1 in the country for amount of money spent on both groceries and dining out.