This summer we had a small garden. We had several different vegetables including a very abundant amount of lettuce. I usually picked it fresh but sometimes when I picked too much I'd put it in a bag and stick it in the fridge. Well one day I didn't have a ziplock to put it in so I used a different bag and oh my gosh did that lettuce last forever (which I know because I had 'found' it in the fridge quite a long time later).
It was a Meijer bag. I know, I know, but I really couldn't believe how long it kept my lettuce fresh and crisp. I mean no slimy goo, no strong or strange smells, no brown or black lettuce, just nice green, crisp, beautiful, lettuce. So since then I've been keeping my lettuce in the Meijer bag. I usually buy a head of green leaf lettuce and when I get home I chop the end off, rinse it, spin it dry, and toss it back in the Meijer bag. While it certainly doesn't keep indefinitely, it will (or seems to) keep longer than in a ziplock and it certainly is cheaper.