I'm constantly amazed by how long Romaine Lettuce lasts unrefrigerated. We store it in the cabin usually hanging in a grocery bag off a wall somewhere. Not even bothering to put it in the bilge where it is cooler, we still manage to routinely have it last a week. We buy three 3 head packages (its the hearts not the full outside leaf parts too) each week that we can. And, usually we're eating the last head or two on the last day or so. I've had it last 10 days but must admit it starts turning a bit yellow and tastes a bit bitter by then.
the three head packs that are washed seem to last much longer than the regular Romaine that you purchase with lots of outside leaves on it too.
I love fresh greens but it is really nice to have a lettuce that will keep, too.