OP - not sure if you're brand-specific but if you are, be aware that the resorts & parks only sell Gerber brand baby food. As of 2008, they did not sell Gerber Organics, but that may have changed.
We used Earth's Best brand so we ordered from wegoshop & were able to choose exact types of food we wanted. We also ordered diapers, wipes, formula & some snacks & water for the grown ups too.
ETA - for baby food at WDW, you will pay double what you would pay in a grocery store.