Greengarden is right about it not keeping long, but I'd avoid a plastic baggy for storage. In my experience this will only give mold/rot due to lack of air movement. Use something like an envelope that will serve to catch the seed, but also allows a little bit of air circulation to prevent mold/rot. You can keep this for quite awhile in a cool dark place, or the refrigerator for longer storage
Ok, I thought I read plastic baggy in the previous post... whoops. nevermind. Stick with the envelope, and you'll do fine.