My mom used a trick that worked - and I found it helpful with Stephen, who is obsessed with bags. She likes to dump small trash cans just to play/lick/make-noise-with the trash bags.
With our dog at home (who liked the trash, not the sacks), we did "tabasco-training". Put a small dab of tabasco (and i mean small) on your finger next time you catch your pet messing with the trash can and touch your finger to their tongue. The reaction of the pet will obviously be unpleasant. Then take a cloth with a little tobasco on it and rub it on the underside of the trash can or around the rim. Next time your pet goes near it, she will remember the bad taste.
I don't know where my mom got the idea, but it works. We even told our vet at home about it - and he said it was a good idea and wouldn't hurt the animal, as long as people didn't abuse the trick. (i.e. -- pouring tabasco down pets' throats).