Geez Joe, you make it sound like he's going to a war zone.....
Just got back from India. I go every couple years to visit the wifes family.
Joes right about the sanitary situation. The wife and I bring little bottles of hand sanitizer for when we are out an about. The bathrooms are typically unspeakably horrible, and I would suggest seeking a western restaurant like McDonalds or a hotel if you need to go while out and about.
If you have alergies, or you have asthma, being Claratin-D or another medicine. I would suggest something with a decongestant. The air pollution is astounding. Bring cough drops regardless.
Don't eat food from little road side stands. It may seem quaint, but you will pay in the end (literally).
DO NOT drink water that is given to you unless it is in an UNOPENNED bottle. I have witnessed a kid sitting in the back of a shop refilling water bottles with my own eyes.