Our family likes to hunt for geocaches. It's a game that suits all ages. Sometimes we hide our own caches too. Occasionally the geocache containers have to be magnetic to stay in place. There are magnetic geocache containers you can buy but we make our own.
This is what you need:
One or more Geocache containers. In this example we use aluminum cylinders with screw on caps.
A pack of Sugru. (Usually enough for four containers.)
A magnet. I prefer neodymium magnets.
And this is how you do:
Open the Sugru pack and knead it warm.
Split it in as many parts as you have containers and magnets.
Glue the magnets to the containers with the Sugru and let it set for 24 hours.
Are you a geocacher? If you hide your own caches, and have an iPhone, you should try my app, Geocache Coordinate Finder. It helps you get good coordinates for your cache by making many latitude and longitude location measurements and calculating an average. It's free.