INDIANAPOLIS - Heading downtown Sunday to pick up groceries for the week, conjoined twins Wendy and Marta Brown were thrilled to discover Walmart's exciting 2-items-for-the-price-of-1 offers. Leaving the multi-national retailer with a cart-full of tinned goods and six packets of Swiss cheese, the siblings smiled broadly, evidently unaware that the sell-by date on each item is the day after next.