I use one of these for that:

Honeywell Fire Safe Waterproof Box, Medium, Model 1103

It's pretty distinctive, i.e., doesn't look like any of the zillion Banker's Boxes around my place - so it's easy to describe to distant relations how to find it.

About 50 bucks. It's not an anti-burglar "safe" - it's easy to open it up. Anyways, it's not that heavy, and it has a handle, after all.

Its purpose is to preserve the contents, until the Fire Department shows up. Compare the rating of the fire chest (this one is rated at 30 minutes) with the response time of your local FD (mine is about 5-10 minutes) to see if it's a match for your needs.