Our advice is to bring as few things as possible since you can buy almost everything in the country on your India Travel.
This is especially true when you are visiting metro cities. Possibly, the only things that are not cheap are equipment that one generally uses for trekking, mountaineering or camping.
Here is a small list of essentials that you may bring with you on your India Travel:
A combination plug that can go in the round-pin sockets. Also, a converter plug (Indian voltage is 220 volts while the US uses 110 volts).
If you are traveling in winter, bring heavy woollens to ward off the cold in the North and with the occasional rains, it become extra chilly.
For summer, sunglasses, a large brimmed cap of hat, and sunscreen lotion or sun block are a must.
Prescription medicines, extra pair of contact lenses or spectacles along with your eye prescription and water purification tablets must be brought.
Budget travelers could bring along a sleeping bag or they might have to rough it out on their India Travel.