Super markets certainly have their problems, for reasons you've said. However, you can choose not to put your groceries in any plastic from the supermarket, if you wish. I have done exactly that for a while now and it's easily doable, you just have to be a little choosy about what you buy.

If people switched to shopping at local farmer's markets - so food wouldn't be shipped around at all - we would produce much less pollution and have much sustainable agriculture than either of those options.