You will definitely have to have your driver’s license and passport, and Uruguay is a little bit easier to get around in without as many restrictions then Brazil.  If you bring your own motor bike, you have to have proof of insurance and ownership, and a special pass to circulate in the country.  You must wear a helmet and some places require and international drivers license.   You must state the specific time that you will be in the country and not overstay that time period.   Different parts of South America demand that you have insurance and it is not easy to get.  You also need a visa, and you may have to offer some people money, at the borders, even though you have documentation.  Read this post that this person wrote about traveling through South America and then, if I were you, I would contact a good travel agency, to find out how to get the documentation you need, and then make several copies.  Apparently, it is common to have border guards keep your information, unless you pay them, and many people have their identity stolen.  Here is the link to the post that someone made, after a trip like the one you are planning. http://roadkill.com/~davet/wt/brad_martin.html.