When traveling to Mexico with a 3-month-old baby, it is a good idea to bring along medications such as Tempra, Tylenol, and Pedialyte as a precaution. These medications can help alleviate symptoms of common illnesses like fever, pain, and dehydration that your baby may experience while traveling. It is always best to consult with a healthcare professional before traveling to ensure you have the appropriate medications on hand for your baby's needs.