You will need a current U.S. passport. While there is no official 6-month expiration rule with Mexico, some airlines may request that your passport does not expire within 6 months of your trip. If you are handed an immigration form as you go through customs, they may hand you the bottom of the form back. If so, you should keep it during your trip, as they will request it when you leave Mexico to fly back home.
We recommend flying into Aeropuerto Internacional Benito Juárez (MEX), which offers the most flight options and is closest to the venue and hotels. Felipe Ángeles International Airport (NLU) and Toluca International Airport (TLC) are farther away.
Taxis are the best option. We recommend Taxi Autorizado or Yellow Cab. They have booths near the airport exit and fixed rates that are posted on laminated sheets (should be ~$400 MEX / ~$25 USD to Polanco / Reforma / Roma / Condesa). The employees working at the booths will hand you a slip, then you can line up by the curb at that company's booth and hand it to the employee managing the line. Tipping the driver is optional, but ~$50 MEX / ~$3-5 USD is typical.
Pants! Mexico City in September has mild weather, so pants and light sweaters or jackets are best. There also is a good chance of rain.
You can use your credit card almost everywhere in the city, but there are a few places that are still cash-only. If you choose to bring pesos, smaller bills are better as they are mostly useful for tipping or small purchases. We recommend exchanging money ahead of time at your local bank. There are also exchange shops and ATMs at the airport.
Ubers are a great and reasonably priced option. Taxis are a good option too, though you should request them via phone from an established "sitio" rather than hailing them on the street. Renting a car is probably not necessary. While Mexico City is huge, a lot of the sights are near each other.
Great question! Yes, the annual earthquake drill ("simulacro") will happen on Saturday at noon. Don't be alarmed if you get an alert on your phone or hear sirens. It's just a drill!
Don't drink the tap water. Convenience stores (Oxxo is a very popular chain) always have bottles of water. Restaurants will always serve you bottled water, but you can double check if you are more comfortable. Ice is ok, but you can ask restaurants to not include ice.
There is amazing street food all over Mexico City. Unlike formal restaurants, food handling can vary, so only eat it if you are comfortable. Generally speaking, busy spots are good options, and cooked food like tacos are much safer than fruit.