Two of the stores I shop at most (local grocery store and Target) both have "cafes" when you walk in. We routinely walk around Target eating soft pretzels and drinking lemonade, but we paid for them. I certainly have used something that I was intending on buying and then paid at the register. Hell, I've even taken a water bottle from Home Goods, shopped, and then paid for it at the register when I was ringing up all my other stuff. I know lots of people that do it and I don't think there's anything wrong with it IF you pay for it before you leave.