IF you're renting a car, there is a Wal-Mart about 10 minutes away from WDW. It might be worth the hour or so out of your vacation to drive there unless Wal-Mart is offering free shipping.
I haven't had items shipped to WDW, but have to many other resorts and hotels across the country. If you are clear in the directions (including such things as "guest arriving on x/y/z" you should be just fine.