Never swap water bottles. Don't eat fruits and vegetables that weren't either peeled or washed in treated water. We'll only dine in places that cater to the stomachs of gringo westerners. If you do get diarrhea please let your guide know so that we can supply you with a little compassion and the best medical treatment available. It is always advisable to carry a stash of toilet paper with you, as all rest rooms are not stocked.
People love presents.
Bargaining is the name of the game, so feel free to haggle with the locals. Carry your money and passport in a neck pouch or waist belt. Look for these at your local camping store. Lots of folks experiment with black and white film and have reported excellent results. This works really well if you have a second camera.