Passport - identification is not required to get into Mexico but if you are planning on returning to the U.S. remember your passport. They wont let you back in without it.
Cash - most of the dental offices with take credit cards, but we suggest bringing cash if you want to purchase any food, drink or souvenirs. In case you forgot cash or maybe didn't bring enough their are ATM's located in the Purple Pharmacy. Expect to pay a Foreign Transaction Fee of at least $10.  HSBC Bank manages the ATM in the pharmacy, but due to identity thief and for security reasons we recommend not using an ATM in Mexico.
Cell Phone - coverage is spotty but you are able to makes calls to the U.S. in case of an emergency.
Friend - If you can, bring a friend. It will be a fun experience and its always good to go somewhere you've never been with company!