 Pepsi said today that sales of its Frito-Lay snacks are down half a percent in the most recent quarter as customers become more value-conscious. Sally Lyons-Wyatt, who's with the big market research firm Cercana, says some shoppers are switching to cheaper store brands, which is unusual when it comes to salty snacks. But it's not all about pinching pennies. Lyons-Wyatt also says people are putting more upscale products in their shopping carts, maybe as kind of an affordable luxury.