India is a vast country with destinations spread far and wide. It is most likely that you will travel long distances whence going from one destination to another. The journey may be by rail, by air or road. Sometimes you have to use all mode of transport to reach your destination.
Most of the distance covered may be overnight journeys if traveling by rail and road. While on travel you need to take care of your essentials, food, medicine, drinking water and interim stays. The weather may be different cold or hot so necessary garments are required. Banking facilities are not available at small places in the interiors so requisite amount of cash in bag is a must. While visiting ancient monuments or other places of tourism guide services may be required. Remember to check the identity of the guide and take reference from the hotel your are putting up at.
Air travel is costlier in India and so are private taxis. The best way to move from one place to another is by train which is the cheapest mode of transportation. You can book e-ticket online now but while presenting your ticket you need to show your original identity to the ticket collector.
Identity proof is required even while boarding a plane. It will be required while booking hotels in India and sometimes at National Parks and trade fairs etc. For foreign travelers passport works fine as an identity proof for Indian Nationals there are many options. Most popular form of identity proof is the driving license followed by the pan card issued by the Income Tax Department of India. Another good proof is the UID Card also known as the Aadhar Card issued by UIDAI. Bills with photograph and address may also work but sometimes the former ones are asked for.
For foreign travelers passport details are compulsorily submitted to the nearest police station. This formality can be submitted on a form in possession of the hotel you stay at. This information may be submitted at many major destinations in India. the information may also be required whence visiting major National Parks and places of archeological importance.