Geocaching is a fun activity for all ages. It involves the use of a GPS (Global Positioning System) unit to find "hidden" treasures. There are many types of geocaches available online or you can devise one of your own. Take a waterproof box and place some items in it such as a pencil, a school spirit badge, something your class has made, artwork, key chains, a book, etc. Hide this box somewhere that you can make a short trip to in order to show your students how a GPS device works. The idea is to set the coordinates on your GPS device and show the students how it works when traveling to the hidden treasures.
(image from Garmin)
Some ideas could be a nature walk, collecting flowers or rocks, observing the different types of trees, looking for animal habitats, collecting different soil samples as well as leaves, etc. Take a camera with you and allow the students to take pictures of what they see. If you don't have a digital camera a disposable one will work fine. GPS units cost anywhere from $100-$300. You don't need anything elaborate when working with kids. You could also take sketch pads so the kids can draw the different things they see.
If you set up the geocaching adventure with several classes you can leave something in your container for each class to trade out. One item could be a disposable camera so each class can take pictures of themselves and leave it in the container. At the end of the school year take the camera and have the pictures developed and show what the students did during the lesson.