In Case of Fire
If you want to make sure your items are safe if there is a fire, buy a fire-proof safe. You can put most of your valuables there, but you want to ensure that the safe is sturdy enough too. The express goal is to also make sure that the safe cannot be carried away by a burglar.
If the safe is portable, it once more defeats the purpose of a safe, keeping it in your house, with your things safe inside. Make sure the fire-proof safe you get is heavy enough that it cannot be easily lifted. One last thing on the topic of a safe: BOLT IT DOWN.