At the very least, a physical cache should include a logbook. Hunters can sign and date the logbook to record their discovery. Many hunters will include a short description of their experience, their impression of the cache or the hiding place itself. Usually the cache will also contain a pen or pencil, since it seems most hunters habitually leave their own at home when they set out to find a cache. Small caches that contain only a logbook are called microcaches.
A larger cache might contain any number of small, interesting objects. Some caches have CDs or DVDs in them. Others have small toys or gag gifts. You might find a disposable camera in the cache. You should use it to take a picture of yourself (or your group) and then return the camera to the cache. If the camera is full, you should take a note of it and let the geocacher who maintains that cache know about it.
Of course, there are some things that shouldn't go in a cache. Food is always a bad idea -- it can attract animals or spoil. Weapons, fireworks, alcohol, tobacco and other drugs or any other questionable or illegal object should never be put in a cache. Since geocaching is family-friendly activity, only appropriate items should go into a cache.
A geocache might contain a second, smaller cache. These smaller caches are called hitchhiker caches. When you find a hitchhiker cache, you sign the corresponding logbook (both for the hitchhiker cache and the overall cache) and you take the hitchhiker cache with you. On your next trip to a completely different cache, you bring the hitchhiker with you and place it in the cache once you find it. You should also look for an email address or other instructions on the hitchhiker. There's a good chance the person who originally put the hitchhiker in a cache would like to keep track of its journeys.
Groundspeak, the company that manages Geocaching.com, sells trackable tags called Travel Bugs that you can attach to any item you want to place in a cache. Like a hitchhiker cache, hunters can take the tagged item and put it in another cache. The hunter is supposed to log the find by going to Groundspeak's Web site and entering the tracking number into its system, then logging the find on the Travel Bug's homepage. Some people create goals for their Travel Bugs, like a journey across the country from one coast to the other. Geocachers are encouraged to try and help fulfill that goal.
Geocoins are another hitchhiker. Geocachers can create a coin as a personal signature to leave behind at any cache they find. Each geocoin has a trackable ID stamped somewhere on the coin. Geocachers can move these coins from one cache to another, or even just pass it along to someone else. The holder of the coin can use the tracking number to log his experiences before passing it along.
In the next section, we'll look at some of the concerns about geocaching and why some places are restricting it or banning it outright.