Can anyone help?? I only shop for groceries twice a month, and usually buy 1 bag of romaine lettuce (or 2 if it's Buy One Get One). I love the convenience of bagged lettuce, but it barely lasts a week. After opening, I use a chip clip to keep it closed up. Does anyone have any advice on keeping lettuce from getting rusty & slimy? Does buying a head of lettuce last longer?