I started some mesclun greens in a container to grow continually all winter. Holy mackerel, has it ever taken off!
I did a second planting but the first one is giving me salad after salad. I cut the biggest leaves whenever I want them and a single seed gives me leaves night after night. Great mini-project for the kids to help them understand where our food comes from. And once they put in the effort and watch something grow you'll be surprised how eager they are to eat it!
I also have cherry tomatoes still on a plant that I can drag in on chilly fall nights.