The BLS CEX has data on average spending in food categories covering grocery spending and spending on eating out. They have tables that break the data down by income groups. The data here is from 2011.
First we can see the amounts that people spend on eating at home and eating out based on income groups :
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I also thought it would be interesting to see what percent of the grocery budget for food eaten at home goes to different types of foods. For example : Do poor people eat more carbos and less veggies as a portion of their entire grocery budget? Or do rich people spend more of their budget on steaks and fancy cheeses?
I found it interesting that there is fairly little variation in the percent of the grocery budget that goes to each category across income groups. The differences in % of total budget spent across income groups varies only 1-3%. For example every income group spends 9-10% of their grocery dollars on nonalcoholic beverages. Now of course we can see from the first chart that peoples spending on groceries goes up with income. However the portions spent in each aisle of the grocery store seems to stay fairly consistent no matter how much you make. So poor people and rich people spend about 10% of their grocery money in the beverage aisle, 22% in the meat section, 11% on dairy, etc.