Here's a handy checklist of things we suggest you bring along when you come to India. While most of the things are available in India, there may be some difference in quality and price. 

Clothes

Cotton trousers.

A pair of shorts.

Long cotton skirts for women. 

Light colored shirts and T-shirts (cotton).

A hand towel.

Good number of cotton underwear.

Raincoat.

A hat.

A sweater for hill stations. 

Sandals and easy slip-ons for frequent removal whilst visiting temples.

Cotton socks to wear when you find the floor at such sites hot.

Slippers if there are frequent long distance train travels. 

A pair of sneakers. 

Swimming gear.

A set of formal clothing. 

General

A small, handy and effective torch to be always carried along. 

A multi-purpose knife set like Swiss Army knife.

Water purification tablets if visiting remote locations where mineral water is unavailable. 

Sunglasses.

Sunscreen lotions (High factor)

A pair of binoculars.

A lightweight bed sheet.

Mosquito repellent or mosquito net (lightweight, permethrin-impregnated). 

Hands and face tissues.

An inflatable pillow. Neck-rest pillow for long bus journeys.

Ear plugs.

Shampoo and conditioner.

Lip balm.

Water bottle (handy)

A small bag to carry essential things while on sightseeing.

Air cushions for hard seating.

Bumbag.

Contact lens cleaning equipment.

Eye mask.

Shower gel.

Nail brush

Short wave radio.

Spare batteries.

Umbrella

Wipes

Toilet paper

Money belt

Medicines

Your prescription medicines, if any, in labeled containers.

Medicine for diarrhea (Imodium, Lomotil) and an upset stomach (Gelusil). 

Medicine for cough and cold, such as pseudoephedrine tablets (Sudafed) and cough syrups (Tossex, Linctus Codeine).

Pain-relieving medicines, such as paracetamol, ibuprofen or aspirin (Crocin, Disprin). 

Decongestants and antihistamines (Avil, Benadryl) for treating allergies.

Antibiotic ointments (Neosporin), bandages, Band-Aids, surgical adhesive tape, sterile gauze, cotton-wool buds, corn pads.

Medicines for preventing motion sickness, such as dimenhydrinate (Dramamine) and anti-nausea drug promethazine (Phenergan).

Anti-infection ointments like cetrimide.

Dusting powder for feet against fungal attack.

First Aid kit alongwith syringes, needles, disposable gloves, scissors, tweezers, nail clippers, pocket knife, thermometer, and mirror.

Chapsticks and vaseline are useful for colder climates; and a steroid cream (Eumosome) is helpful to relieve the itching caused by insect bites.

Condoms and contraceptives.

Documents

Passport and VISA. Keep separate photostat copies.

Confirmed air tickets for all sectors.

Clearly filled up vouchers of your tour operator with all service details.

Name & contact details of next of kin.

All confirmed hotels names and addresses.

Confirmation faxes/letters/e-mails from tour operator, hotels and other service providers already booked.

Complete information on itinerary, sites, and important places of assistance. 

Spare passport-size photographs

International driving license.

All permits, Indrail passes and other documents if applicable.