Vacationing out of the country with an infant?

Has anyone out there been on vacation out of the country with their infant? My hubby and i were asked to go on vacation to cancun mexico with my husbands side of the family in December but our baby boy will be about 4 months old... First time mom here.... But my husband and i have traveled all over the world so we r use to travel... Just not with a baby yet! Any advice would be great thank you!