In Argentina and Uruguay, you might see people carrying a thermos tucked under their arm. It's their version of a Starbucks cup. The thermoses carry hot water, which is used to refill beautiful gourd cups of yerba mate (pronounced 'mah-tey'), an herbal tea. Yerba mate is a plant in the holly family, and its dried leaves are believed to have stimulant properties similar to coffee, but with fewer side effects.
In South America, drinking yerba mate is a very social activity. Tea drinkers brew the mate in beautiful gourd cups, and sip it with a silver straw called a bombilla. There is a ritual way of preparing the leaves and steeping them in the water. You can see a great slideshow on how to do it here, from a website that sells the gourds and the mate tea. This special steeping method allows mate addicts to drink from the same leaves all day. In fact, avid mate drinkers carry thermoses of hot water around to refresh their tea.