Before returning to the United States, you should understand what is legal to bring through U.S. Customs. Just because it was legal to buy that box of Cuban cigars in Spain doesn't mean that you can legally bring them back to the U.S. Visit the U.S. Customs and Border Protection's website for U.S. travelers.
Also, be prepared to experience "reverse culture shock," (a.k.a. Re-entry Shock) upon returning to your home culture after growing accustomed to a new one. The best way to avoid these feelings is to stay international. Meet other international students that are studying abroad at MSU and help other U.S. students go abroad!