Hi Patricia!
Unfortunately, I have to say I've never heard of a shuttle or bus from a Walt Disney World resort to Walmart.
If you'd like to do some snack or grocery shopping, there are two options I can think of:
- Choose from the snacks and small grocery section available at the resort's shop
- Opt to take a taxi from the resort to Walmart and/or other grocery store and back again
Personally, once I arrive at Walt Disney World I hate to take time out of our limited vacation time to head to Walmart. In general I avoid this at all costs - BUT I know it can be quite a money saver, so you'll have to balance the cost and time factors.
Don't forget, there are some snacks you can pack in your suitcases as well. Non-perishable granola bars, breakfast bars, etc make good grab and go options that could work for you. And, the bonus of this is, after you've eaten them all you'll have some extra room in your suitcases for souvenirs!
Hope this helps!