The Data Cart is a way of storing treaties and countries that you want to work with later in a session. For example, if you want to compile a list of treaties dealing with Protected Areas and some additional treaties, you could first use the Treaty Locator to search subject = Protected Areas. Once you obtain the results set click the ++ icon to add all those treaties to the cart, and then search the database for the additional treaties you are interested in, and check the boxes next to those treaties to add them to the Cart. If you now visit the Data Cart you will have all the Protected Areas treaties plus the additional ones you just selected. You can then click on Summarize and Download to display basic information about those treaties (year of agreement, number of parties, etc.) and then download it in a comma-separated value (CSV) file.
The Data Cart can also be used to create a Treaty Status Matrix, in which country participation in selected treaties is listed. To learn how to create a Treaty Status Matrix read the Q&A entry for How do I create a Treaty Status Matrix?
Note that items in the data cart are not persistent between sessions.