We have in the past rented a car at the Dolphin from Alamo and driven to the Super Wal Mart. It is about 5 to 10 minutes away from BWV. This has worked out very well for us. We get everything we need and they prices are great nothing is over priced it is the same Wal Mart prices as they are here at home.
From BWV, take a right out of the resort, left at Buena Vista, continue past CBR and Bonnet Creek and take the exit to 536 (Epcot Center Blvd). Get into the left lane on 536 until you pass the I-4 exits. When you get to 535 turn right for the new Walmart, it's about a mile down the road.
I just found out that the Hess only sells Coke products and we love our Diet Pepsi. We are going to mail our groceries (only $7.70 for a flat rate box no matter the weight) and then buy bottles of Diet Pepsi at the airport and put in one of our carry on bags.