It is far better and cheaper that you get most of the Mexican pesos (MXN) here in Mexico than abroad.
Nevertheless, if you haven’t booked the very first services in your first day in Mexico, such as transportation (your taxi from airport to hotel, for example), meals (meals in hotel, but what if you are already hungry when arriving), then i recommend to change $1000MXN, especially in change (200, 100, 50). Don’t get a $1000 bill, since, almost no one accepts it or it will be difficult to get change it to low value coin / bill.
The rest of the money you use, change it here in Mexico, you can use an ATM specially once. In money exchange offices, the rate and comissions are high.
The rest pay with debit/credit cards where available.
I recommend you to use 40%, of all the money you think to spend in Mexico, in cash. And 60% in (debit) card. Yeah, visa and master card are widely accepted in Mexico. You can use your card in shop, restaurants, stores, online, … where available.
One thing is that in Restaurants you should verify if the bill already includes the tip. Otherwise, usually you give around 10% of the price. Sometimes you can say, “i just want to pay the bill with my card, and the tip i will give to the waiter / waitress in cash”.
As for the Forex (november 2014) money exchange rate, 15,8 MXN does not sound to be a nice deal. In the bank i use, they sell the euro at 16.9425 MXN. So Forex sounds more expensive. Here is the website of the bank with the table of currencies for Mexican Pesos:
http://www.banamex.com/economia_finanzas/es/divisas_metales/divisas_mundiales.htm
Read the column “Compra” (buy). This table is updated every day.
On the street, use cash.
If you come from Europe, Asia, Australia (Except the Americas) You will require adapter for both your cellphone and camera (European to American plug adapter). In Mexico you can get it in the airport but it may be really expensive (like 60 or 90 pesos). You can buy it cheaper in stores such like “Steren” or “Radio Shack”.
Whether in Mexico city during winter
(November 2014) Well, it’s been very chilly for us lately in the mornings, but there is sun and it burns fine. But if you stay under a tree or in the shadow of a building, you start to feel cold again. The wind is cold now in Mexico city. So, you can, of course take your summer clothing 🙂 But bring a jacket and a scarf for the nights and mornings.
Yes! take sun screen 🙂 The sun burns though!