For them to last and function when needed, distress lights must be kept away from any moisture. A waterproof plastic container is not a bad idea. They shouldn’t get thrown around too much, to avoid physical damage.
Keep them away from heat sources, especially the pyrotechnic ones. They can catch fire and cause serious damage. When your flares have expired, don’t just throw them in the trash, they can present a hazard. Be sure to contact your marine authorities to learn where and how you should do this.