Keep the film in a cool, dark place so that it does not warp and deteriorate. Most pack film will last at least one year after its expiration date if kept cool in the dark – and that shelf life may extend for three years or more if you store your 600 film in the fridge. Take the film out of the fridge and let it warm up for about an hour before you load it into the camera.
Do not freeze the film! This may damage the film and will not lengthen its shelf life. If you are using old, questionably-stored film with a long-past expiration date, be aware that your photos may or may not come out. It doesn't hurt to try loading the film, even if you aren't sure!