I don't like monkeying around trying to find someone to break up bills or find a working/trustworthy cash machine. I've also had problems a number of times getting specific (especially small) currency notes in any denomination in Mexico...even at the banks. So for the last several years, I just bring what I feel I'll need in specific denominations and stick mostly with US currency...For a couple of my 10+ day trips, that was a big wad of notes, but I've never had a problem with TSA over it. Then I bring maybe three hundred in 20's for anything outside of the resort and for any trinkets. In the natural course of doing things, I'll usually run across a cash machine that I'm willing to use, preferably at a bank, and hit it up for a thousand or even two in pesos just to have for anyone who prefers them...but I don't go looking for it. I often end up bringing most of that home with me. My math for currency is 20 singles per day for drinks, four five's for the maid and meals, some extra fives for the baggage hauling, transfer drivers and such and a few tens for anything out of the ordinary. Generally that works out to around $50-55 a day-for 1 person...presumably a couple would have a different ratio for some of that...but I usually bring some of that home too. I never then have to think about what I'm going to buy or tip what with and don't have to go find someone to break a $20 on that last day.
You are right that the new ones are hard to counterfit, but nobody still takes them. So if you have a fist full of them then you will have major worries. Jamie
I'm right with you. It's kind of fun to get a large amount of money in small bills. About a decade ago I had trouble receiving correct change; I carry a lot of smaller bills. Anything over a $20 is useless to me in MX.
canadiens should exchange their dollars at the cambio across the street and to the left as Jaime stated. US should bring the wad of singles and $20s for other excursions or shopping as Nate said. The ATM at the small convenience store has a much better exchange rate than the one at TTR.