There is a Publix off 535 about 10 minutes away. At the crossroads turn right for about 5 miles (I think) the Publix is on the right. It's on the corner of 535 and 129 (another I think that's the road that 535 leads into). It's behind a Burger King.
Also, there is another new grocery store closer to WDW called Winn Dixie. Make a left at Crossroads and it's about a mile on the right.
Hope this helps, Beth