If you're driving, park at a meter on John McCormack Road, or hypothetically press your luck by parking on campus. You'll only be there for 10 minutes, so why not live on the edge and risk a ticket? Walk to the Pryzbyla Center, using parking garage stairs as a shortcut through campus, and go up to the 2nd floor - voila. Order what you want and be on your way. I usually go for the off-menu cafe con leche (or cafe au lait if you're feeling more continental), which means I get to explain to the barista that I'd like coffee and not a latte. To get back to Michigan Avenue you'll need to cut through campus, exiting at the front of the Basilica.
* credit where credit is due, the image comes from http://1stincoffee.files.wordpress.com/2009/10/espresso_coffee-machine-making-espresso.jpg?w=300&h=300