Nahuatl Woman at Day of Dead celebration, Tamazunchale, SLP
Good for you! If you are concerned about that, you probably aren't one. Your camera's not the issue. Cameras don't make stereotypes. People do. Most people are happy to have their picture taken. However, nobody likes being treated like an animal in a zoo to be gawked at. Before you shoot anyone (with a camera!), smile, point to the camera and to them and see how they react. 90% of the time, they will smile back or nod yes. You are ready to go.
The oft-repeated “generally accepted” statement about shooting pictures in Mexico is that you shouldn't carry an expensive camera since it will be stolen in a heartbeat. Like any myth, there is some truth to it, but very little. I've traveled with professional reporters (including a National Geographic photog whose gear was worth more than the trailer I lived in) to small towns, slums and big cities. Not once were we accosted. That said, just as in the USA or any country, high-crime areas are best avoided. I walked into what used to be East Berlin and shot all day. It was a sketchy neighborhood and I did feel uncomfortable, but not enough to leave. Your sensibilities (and general common sense) may be better than mine, so listen to them.
Lose your charger? Need a special battery for your cameras? Need just about anything electronic or camera-related? Unlike years ago when you were just SOL, you now have options.
For really esoteric stuff like chargers, filters, caps etc., there is a second-hand flea market specializing in photo and computer and electronic gear. I lost a Lumix charger once. Found a new one there. Needed EN and EL batteries for my Nikons. Yep. And so on. Just ask around for the Tianguis Electronico or even Mercado Electronico and you'll find one. From what I've read, these marts exist in Asia too. OK, sometimes the gear is stolen. Then you have a moral dilemma. But how would you know? Well, if you see your camera that went missing a few days ago, I guess that would be a clue. Seriously, if your gear gets stolen, try looking at one of these markets.
Best Buy is in every major city and is often pretty well-stocked. It is hit or miss depending on the city, but you'll find a lot of items there. Amazon now ships to Mexico.
Office Depot / Max is even more common and they have limited photo gear and always have SD cards (tarjetas de memoria or simply SD Cards).