I find lettuce stays well in a plastic bag that's not closed too tightly, if I spray in a bit of water every couple of days to keep the humidity up.
Jokerama, I had the same problem as you. I've been much better since I started shopping for perishables much more often. Yes, I spend more money on gas running to the market every other day (6.5 miles away from me). But I'm certain I save more than that in not wasting expensive organic food. Plus, I try to think out other errands that I have to do so I can combine frequent grocery trips with them. That way, I'm not running to the bank one day, the grocery store the next, the garage the third, and the grocery again the fourth day. Rather, I'll do the bank and grocery one day, and the garage and grocery on the third day.
Currently, I drive really far once every two weeks for almost all my dairy and meat, plus bulk items and some convenience items. In between, I go to the local organic market for produce and a few fill-in meat and dairy items. I also make up large pots of things like chili and soup, which allows me to have a bunch of healthful meals prepared without having to worry about keeping perishable raw foods around and forgetting to use them.