Either opportunistic or exploitive are appropriate -those words are not always negative, to me they also have a descriptive meaning. If they saw a trend and they took steps to fulfill the foreseen demand, it's all good. I'm sure people were happy WalMart had that in stock, rather than think 'this WalMart, they're using this hurricane in an underhanded way to sell me more poptarts'.
There's plenty to dislike about Wal-Mart, but there is absolutely nothing wrong with predicting a sudden shortage of a product in a particular area, and trucking in a bunch.
If they'd doubled the price, that would be another matter, but that's not what they did.
Pop-Tarts are a cheap, readily-accessible, easily-consumed source of calories with a long shelf life that most people will at least tolerate. They're nutritionally incomplete, but they will help keep you alive and functional in the short term.
Most people don't stock up on MREs and survival bars, nor even have a clue where to start. Under such circumstances, it's both expected and reasonable that they reach for a familiar, readily-available energy source.
I remember hearing an anecdote many years ago that when food supplies where being dropped over Afghanistan it was the pop-tarts and peanut-butter that were the most popular.
