Always remember to pack light so that you can travel light as India is a country where you will have to manoeuvre through lots of people and less spaces at times. It is advisable to leave space where you can buy clothes appropriate to local weather conditions. Also, formal wear is not required and can again be bought as per need.
Most travellers require a VISA to enter and stay in India. It is always advised to plan in advance about your visa requirements and the timeline is kept in mind. Other documents like tickets, international driving license (if needed), confirmed air tickets for all sectors, clearly filled up vouchers of your tour operator with all service details etc. should also be carried with you.
As in India, there is no set rule of having signboards or directions, you have them at some places and do not at others. Thus, it is imperative that you carry proper maps of the places you wish to visit in India.
Do carry your prescription medicines, if any, in labelled containers. And some specifics like medicine for diarrhoea and stomach disorders. Also, you should carry medicines for cough and cold and cough syrups and other specifics depending on your country of origin. It is better to research before travelling as foreign tourists are susceptible to such diseases as the climate in India can be erratic.
When travelling to India it is best to carry your own electronics or personal gadgets like cameras, phones and their related accessories etc. As, it is not wise to depend on the local markets as the prices may differ variedly and you may or may not get the required parts as well.