The simplest, and yet the most essential item to pack for India is your Passports should have at least six months validity from the date of arrival in India. There should be minimum two blank pages for stamping by the Immigration Officer.
All foreign nationals require a visa to enter India. You will need to obtain a 6-month tourist visa or a 60-day tourist e-Visa. The tourist e-Visa is available to most (but not all) nationalities. However, please be aware of fraudulent online Indian visa websites and only apply through the official website: https://indianvisaonline.gov.in/visa
The six-month multiple entry tourist visa will require submission of your passport along with the completed application form, 2 passport photos and any supporting documents to the nearest India Visa Application Centre on the scheduled date of your interview. The instructions for completing the form and scheduling the appointment can be found at https://indianvisaonline.gov.in/visa
Please note it is NOT possible for British and US passport holders to apply for a visa on arrival in India.