In most circumstances, I would pay for it. This has happened to me a few times, and I usually take the honest route. Once though, I accidentally walked out with a bag of cat food under the cart. I was really broke at the time, and had barely enough money to buy it and the few food items I'd gotten for myself. Ashamed to admit it, but I just kept walking...but it was also late at night, and there was only one clerk on the registers. I knew if I went back in, she would get in trouble for not checking under my cart, so I rationalized to myself that I was helping her out.