This is interesting. There is a real psychological disconnect between your finances when purchasing with a credit card verses cash.
You spend 12-18 percent more when you swipe your card than when you use cash. McDonalds observed their average transactions rose from $4.50 to $7 when customers were allowed to use credit cards to make their purchase instead of cash. Research conducted revealed people spend more when they use their cards even if they paid off their credit card balance each month.