Shopping for food at wal-mart near WDW is like Black Friday every day. It's awful, there are usually whole families meandering through the aisles, not sure where anything is, and generally it's a mess.
We love the Winn-Dixie, it's small enough and really close to the DTD exit, just make a left. I got a discount card in advance and checked the ads on the way down so I have a complete shopping list.
Last trip we used wegoshop.com. Wonderful experience, but you have to be flexible in what you get, like I asked for 2 packs of chicken breasts and got 2 3 pound packs. Too much! Next time, I'll give a weight limit. Otherwise, I got everything, in the right quantity and the right brand. I shopped the store ad so I picked out sale items, B1G1, that sort of thing. It was great and worth the extra money to have it delivered to my door, saved time and aggravation.