Hi Heather,
Great news. Disney World wants to make your vacation as stress free as possible and they have taken into account, a guests' last minute needs. You can purchase basic items like cold and headache medicine, shampoo, toothpaste, diapers and a small selection of food items like doughnuts, bread, cereal and soda from any of the Disney World resorts.
Each resort has a small sundry area that will offer a selection of the most common items that guests forget, run out of, or simply decide they need once on vacation. The area is located inside each of the merchandise/gift stores at each resort and is available as long as the gift shop is open. The selection is small and the prices are slightly higher but you will be able to cover your basic needs. If you anticipate needing an assortment of items, would prefer a larger selection or a slightly better price, you may want to consider ordering your items prior to your vacation. There are a number of stores that offer online orders and delivery to the Disney World resorts. The one I prefer is
www.gardengrocer.com. You can select your item prior to your vacation arrival.
Hope this helps keep all your needs covered. Have a great time!