A couple of things you can do here, Pat. One of the best security measures for the backpacker is to get a PacSafe security net, a stainless-steel mesh bag that fits over your pack or duffel. This will eliminate slash-attacks, and, when inside the PacSafe, the pack can be locked to a handy post or other immovable object. It won’t stop the nimble-fingered and well-equipped thief, of course, but it will vastly cut down the chances that your pack is sliced open or grabbed when you’re not looking. It comes in three sizes, small to large, and sells for $55 to $70.
The best safety device, of course, is prudence. Assuming you’re going on your own聴not as part of an organized group聴check with professional outfitters to see if they have advice on safety precautions. Also talk with people in the U.S. embassy once you get to Peru, as they should be able to tip you off on particular hazards and crime hot spots.
As for yourself, the best thing to do is never look like a would-be “victim.” People looking lost, confused, and exhausted, or with their nose buried in a map, are easy prey. Simply practice looking like you’re not to be trifled with. And, keep money, credit cards, passport, and other valuables on your body in a money belt or under-the-shirt security holster (for example, Eagle Creek’s silk Neck Pouch for $20).
But mainly, have a great trip!