Walmart's main theme is cheaper than anyone else. It achieves this by scales of economy, it buys in bulk and ships with company owned trucks domestically. Walmart is the biggest and smartest retailer-wholesaler-distributor ever conceived. They can view real time cash register readouts in any store, they can compute profitability on a item purchased in a 5 second window.
If Walmart raises their price because of fuel and products (plastics), and the U.S. consumer decides $6 a gallon gas is too much what happens to your neighborhood? I think people will bike, walk, or bus to the closest store. People will demand lower prices and local producers will fill the void by minimal to market transportation. Sounds crazy? Think micro-breweries and farmers markets.
Perhaps in the future with expensive fuel, house hunters will ask "Is it close to the store and are there sidewalks to school" and "Why is the 2 bike garage so big "?