We were in Windsor Hills (nearby) and there are 2 Walmart's close by. We kept going to the one directly on 192 at marker 15 (I believe Emerald Isle is at around Marker 5). It's a good 15 minute drive but if you stop there on your way in, it might be handy. There is also a lovely new Target on 192 at around Marker 12 (just past Celebration).
If you come down 417 from the airport on the way to EI...there's a Walmart on the map here...it's probably the same one not sure of the exact location, but it would be on your way from the airport. The one off of 27 isn't on the way....it's more like out of the way (but that's the one usually go to once we're there).