The Journal of Consumer Research figured out a way to help you save some money AND cut back on junk food purchases by up to 70%!  It seems that paying CASH at the grocery store decreases the amount of junk food you are likely to buy.  This is especially true if you withdraw the cash from the bank directly before you go shopping.  

According to the study, paying for groceries with your debit card decreases "wallet pain" at the register.  Less "wallet pain" = more impulse buys and poor food choices.