If they can spend the time to harras people as they shop, they can spend the time to search their bag at the checkout. Anything small enough to be hidden enough to avoid such an inspection in a pack could just as easily be put in a jacket or pants.

Concern over bombs in packs is outragiously stupid. Messengers wear packs into far more tasty targets than a grocery store, many bombs are strapped directly to the person of a bomber, and students wear packs all over the liberal-factory university campuses. People even drive cars right up to stores, sometime even parking them underneith. I know that I could fit a larger bomb in a car than in a backpack. And besides, isn't the whole thing about terrorism linked somewhat with the oil thing? Use of backpacks instigates the use of bikes, which despite any psuedologic some throw out, do use less gas than cars.

I have seen people with guns in their pants, I know you can put acid in a cup, knives fit in boots, I have carried a deadly shuriken in my front chest pocket, babies can be loud, poop can stink and contains fecal coliform bacteria and that can kill you.

The stores I go to prefer you to bring your own pack so that you save the use of a disposable one at the checkout.