2. Passport
Another no-brainer, but also not as straightforward as you might think. Your passport cannot expire within 6 months of your return flight from Mexico back to the US or you could be denied boarding. Mexico does actually have an agreement with the US to extend the expiration on the passport by 6 months, but it’s better to be safe than sorry and renew your passport prior to your trip if needed. More information can be found on the Customs and Border Patrol website here: https://help.cbp.gov/s/article/Article-905