Really, it's less a matter of how big the package is and more a matter of how you use it. (Where have I heard that before?)
Scenario: I'm not the mother of 5 and I have no business. I am, however, cheap. I buy the jumbo size of stuff at Costco and what's on sale at the grocery stores -- only the things I use regularly -- in bulk. I shop infrequently and in large quantities, thereby avoiding a number of impulse buys. I spend the time to individually package stuff up -- a big-ass ziploc bag and some wax paper goes a long way in my world. Then I freeze it and thaw what I need as I need it. That way I don't have to go to Walmart. But there I'm lucky -- there are other stores here, and so I just don't support them because I don't have to, cheap or not.
Someone here posted that where they're at Walmart is the only show in town, and that, IMO, is really the problem, not having one in a city like Seattle. When a Walmart is the only shopping, it's also the only signifigant source of low-income jobs. Then you get the vicious circle where people don't make enough to survive, and they have to shop there because it's close and cheap and they can't get out of the cycle of poverty into which it puts them.