Your plane ticket and a passport.
To buy the plane ticket to Mexico, no... there is no ID required. But to USE that ticket and GO to Mexico then yes, you will need a passport and that will be your ID.
No. If you enter Mexico by plane you need a valid passport. If you enter Mexico by land however, it will not be much of an issue; however on your way back to the US you will have to show at least an ID or birth certificate.
Yes, you do.
There are a couple of answers for you but no matter what you need an ID for all answers I'm about to give. If you travel by bus, or any automotive you need a U.S. Naturalization Citizenship document and if you travel by plane or boat you need a passport POSTER: In response to your question. So, if you are a U.S. citizen, once you are actually in the country of Mexico, you still need to provide ID to go from one part of Mexico to another? What if you are a Mexican citizen who ONLY wants to travel within the borders of Mexico. Would he need an ID?
No. Arms and ammo are illegal in Mexico.
does a citizen of Mexico need a passport to go from the us to Mexico and back? He is legal to be in us but not a us citizen.
Plane
Yes. Not a passport per se, but you need an ID to get into the plane.
get plane tickets and fly to mexico
True: Australia is on the Southern Hemisphere, while Mexico is on the Northern Hemisphere.
Indeed.
Not to mock you, but you can go to Mexico by foot if you want, however from New Jersey to the closest City in Mexico (Nuevo Laredo) you have to travel 1645 miles. On airplane it would take you a bit less than 5 hours, while 'walking the walk' it would take you some 23 non-stop days.