There's a hidden world beneath your nose filled with 2,709,919 objects waiting to be found by those who are in the know. Using the Geocaching app my daughter and find little containers left by geocachers in all kinds of places around the country – even in little Arizona towns in the middle of nowhere. It's like belonging to a secret society.
So far we have only looked for geocache containers, but now we want to start leaving our own geocache containers for others to find.
I ordered a Micro Snap Top Geocache Container 5-Pack for $(removed) on Amazon. They are watertight and include a paper log for people to fill out when they find it. [UPDATE: commenters alerted me that these are just centrifuge tubes and you can buy them for a lot less on Amazon. I canceled my order and got 50 tubes for $(removed).]
They are pretty tiny, so we are trying to figure out what kind of trinkets we can put in them. Perhaps a more experienced geocacher will let us know.