I travel in Mexico a bit and have a few suggestions.
First, don’t worry. You are entering a country with much less crime than the US. Yes, there is petty theft, but violent crime is not an issue. Forget about not looking like a tourist. I can spot an American in a burlap bag at 100 yards. Besides, all the kids in Mexico will be carrying backpacks with American sports logo’s anyway.
Don’t take anything that is “aggressive”. Like big knives or military looking items. Be sure you have no fire arm related items. Not even one bullet in the corner of your pack. No illegal drugs. Your passage into Mexico will be quick and un-eventful. They want you to come there and are not out to hassle you.
On the other hand, be prepared for a hassle when you return to the US. If you live in Texas you know what the Immigration police are like. Well x10 for when they are checking you as you re-enter. Be sure you do not exceed the various limits for items like booze or dollar value of things purchased in Mexico.
Petty theft: Yes, this is a fact of life. But think of it as a game. Most poorer nations look a persons worth as a function of their wit, not their assets. If you are dumb and leave your stuff un-attended, then you deserve to loose it. If you over tip (shows you are foolish about money), are aggressive and demanding, they will respond with clever tricks to humble you. However if you are open, warm and genuine, you will find a people that can teach you a lot about life.
If you feel un-secure about carrying your backpack, put it on backwards. Wear it in front of you. Especially on crowded streets or standing on busses. Don’t wear expensive jewelry or watches. They will “fall off” in a crowd.
All that said, keep you eyes open and really look at what is in front of you. Notice that you will never see a child hit or even addressed with anger. Even if a child lives in a hut with a dirt floor, the kids’ clothes will be spotless. Notice the genuine warmth that people have for each other. If you can learn to drop your American “hardness” they will respond by including you in their lives.
It has been many years since we have traveled in the Copper Canyon area and I suspect things have changed. However you will be entering another world, one that you will not see unless you look. Let you children be your ambassadors. Children are revered and can provide a gateway to the other world. But be careful; do not become angry with your children, ever... This shows you are not worthy as a parent and you will be treated accordingly.
In a sense, it too bad that your tip to Copper Canyon is your first encounter with Mexico. It usually takes a trip or two for Americans to begin to understand that there is a much different way of living than that which we take for granted.
Enjoy... It will be an adventure, not an adventure of “threat” but an adventure of learning.
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...........From Nomad.........Been "on the road" since '97