Your first survival need is air. During disasters such as an epidemic or pandemic you may need to quarantine yourself and family. However, if you need to get supplies you will need protection from infection. Gas masks are the best portable filtration system for your money. If there is ever nuclear fallout or chemical warfare they will be essential. Even with natural disasters such as volcanic eruptions the air can become toxic. You might also want to have a room or shelter with a HEPA air filtration system for tasks where a mask would get in the way.