In India trains are a cheap and very efficient mode of transport. It is the largest railway network in the entire world. More number of people travel by train in India in a day than most other countries combined. Though they have a retro look, railways are fully functional and other than Wifi you get pretty much anything you usually get anywhere in the world. Of course, this depends on the class you travel in.
If you are travelling in India for the first time, it would be best if you go for the 1st AC or the 2nd AC class. If you have travelled before you can go ahead and try 3rd AC or even the non AC Sleeper class. Beware of crowding in the sleeper class though. The cost of each class can be understood from the names.
Irrespective of which class you are travelling in there are some things that you absolutely must carry with yourself.
Wear Comfortable Casuals – This holds true for any part of the world and especially so for the hot and tropical weather of India. Wear casuals and you won't have to worry about your suit getting soiled.
Wear chappals or sandals – Chappals is the Indian variant of a sandal. You can easily wear and remove them. Boots or even sneakers will give you a hard time to manage if you get an upper birth.
Drink less water, Eat less food – Try to drink less water than usual! You may want to avoid the toilet as much as you can. It is true that the trains have become a lot cleaner than what they used to be, but even then avoiding a public toilet is always good. Same goes for food as well. But it is not hell and you won't find something very disgusting either. If it's needed feel free to go. If it is very unclean, kindly notify the guard or any other train official and it will be cleaned in the next station. Also most trains allow you to travel laterally from one carriage to another(legally!) In that case you can find a cleaner toilet anyway. Each carriage also called a kamra in India has 4 toilets – two Indian style and two Western style.
Carry as little luggage as you can – Little luggage always helps. You won't need your teddy bear when you are travelling. Take only what is necessary. India is a reasonably modern country. If you need a deodorant, or soap or anything else, you can get it almost anywhere. In trains the space is limited and carrying a single backpack and a small hand luggage should suffice for anybody. If you can't take a backpack, carry a small suitcase that can fit inside the 1st bunk.
Carry an inflatable pillow – Indians can tolerate a lot of discomfort. If you can travel rough carry a spare pillow or a neck rest. They usually provide only one pillow per person, and that can be inadequate for some. An inflatable pillow takes less space and works great.
Paper soap – You can use them when needed for some basic toilet use. The toilets have soap, but if you feel uneasy paper soap is available about in any station in India.
Tooth Paste – For the morning brush carry this and whatever else you need.
You should not need anything more than these things. In most cases these would fit in a side chain of any bag you might be carrying. Above all board the train with an attitude of “I'm loving it”. It is usually a wonderful though retro experience. Have a safe and happy journey.