Another type of geocache is an "Event Cache". An event geocache is posted on Geocaching.com like a regular geocache, but it's a meet-up of some type. Some "Event" geocaches can be as small as a few geocachers meeting at a local diner on a specific date and time just to have a bite together and swap stories, or it can be on as grand of a scale as a whole weekend event with people camping over, activities, t-shirts, cookouts, games, etc. Here is a picture from a fun "Event" geocache we attended over the summer called Tri-State Treasures Two (you can see the actual geocache page here and read more about it if you want) to give you an idea of how many people attended.
At larger events the person who organizes it usually hides some new geocaches and the coordinates are released first to those attending the event before it gets published to Geocaching.com, so there's the fun of finding new caches as well. Usually at any event, big or small, people bring travel bugs and geocoins to trade and "discover " (you take down the number and log it as "discovered" but you do not actually take the item). At the Tri-State Treasures Two event there were probably about 30 travel bugs brought for "discovery" and trade. At this event there was also a raffle with many prizes like t-shirts, ammo boxes, geocoins, etc. There was also a ton of food. It was a lot of fun! (Kudos to CaptainMath for a great event.)
Event caches are a great way to meet other geocachers in the area and ask questions, swap stories, and just to put faces to the names. Geocachers tend to be fun, friendly people, so if you're thinking of attending an event but are afraid to go because you don't know anyone, you should go for it!
Here's an event geocache that is coming up for people in the southern NY - western CT - northern NJ area that you can check out. It's put on by a well known Hudson Valley geocacher - MSTzilla. It's called the 2008 Mid-Hudson picnic - it's waypoint is GC1GXEA and it's here. It's sure to be a lot of fun, and it's at a park with a great playground so it'll be fun for the kids too. A lot of families geocache, so usually all these events are very family-friendly. MSTzilla mentions that he had geocoins minted for this event that will likely be given out as prizes or released - so if in your geocaching travels you ever pick up one a coin that says, "2008 Mid Hudson Picnic", think of me! :-)