Make a durable time capsule w/ letter, try to find a cave to hide in w/ my nearby friends and family, stock up on resources as best as I can (including tools). I'd be lucky to get that much done so I'm not worried about anything else. Plus, if humanity is actually destroyed (including ALL of its constituents), then the only thing that will make a difference is the time capsule in case aliens or a new sentient species stumble upon it.