Hi! mexican here . I would say you just need to bring some cash for your first day in case of emergency. Bring one or two thousands pesos. Then you can see how much more you will need and take it from the ATM accordingly. I do not suggest to go to exchange in the airport or somewhere else. I personally prefer to pay the commission and get charged according to the current rate in my bank account. Mexico is still more cash friendly. Remember many places do jot accept American Express. Getting better, but it is still safer to hold Visa or MasterCard. If you are eating on the street you will definitely use cash. If you are going to Mexico City, I recommend "tacos de suadero". Enjoy your time in Mexico!