I think what you read was that many of the car services will make a grocery stop on the way from the airport to WDW for up to half an hour for free. Tiffany, Happy Limo, and Yourride.net all do, not sure about Mears and some of the others.
Disney doesn't offer free transportation to anywhere off their property. IF you are taking one of the above car services between the airport and WDW, just ask. OTherwise, you'll have to take a cab, and that's expensive. There is a NASTY Goodings at the Crossroads plaza (end of Disney Hotel plaza area) but IMHO the prices are so high you're better off not dealing with the hassle and just buying at WDW. The general store at the Boardwalk has a decent selection and the prices aren't terrible on many items.
Anne