I've open carried at the Pascagoula walmart quite a bit with no reaction from the public or police - except maybe a few doubletakes.
Walmarts official policy is to follow what the state law allows for whatever state the store is located, this has been discussed many times and the search function is your friend on that subject.
Most law enforcement officers think you must have a permit to open carry, so if you can get one, I'd recommend it. If you cannot get one, then make sure your handgun never gets covered by any clothing or whatever and a voice recorder would be recommended. Also wouldn't hurt to have the OCDO member gunluvnatty (spelling may be incorrect) on retainer.