Our personal experience
After a somewhat expensive taxi ride (200 Baht/ 5,10 Euro*; because we were traveling with a dog) we arrived at Bangkok train station to catch the night train of 6:30 pm (18:30). Since we left our guesthouse near Khao San Road quite late in the afternoon we accepted the more expensive taxi ride. Adding to that, you must not underestimate traffic in a city. Rush hour delayed us for a little bit, but we arrived an hour early. Unfortunately the 458-508 Baht/ 11,69-12,96 Euro cabins for overnight sleeping were already fully booked. We decided to take the 2nd class seated chairs instead for 358 Baht / 9,14 Euro. After entering the train we discovered that the 2nd class seated chairs were actually pretty comfortable. There is enough space between the leather chairs for your feet and the back part of the chairs can be adjusted, comparable to seats in a plane.
The trip from Bangkok train station to Surat Thani will take about 12 hours, so we departed at 6:30 pm (18:30) and arrived in Surat Thani 06:30 am the next morning. The train station has a small supermarket, some vendors and small shops that enable you to but food and drinks for the trip. You can buy drinks and snacks, but these are also offered by people selling them on the train. They will come by a lot! They even provide you with dinner, so do not worry too much about that. You can just buy dinner on forehand or buy it while on the train. These meals are pretty simple, such as rice with egg, chicken and vegetables for 50 Baht / 1,28 Euro. There is no possibility to hop off the train and buy food.
– Make sure you are a couple of hours early if you want a cabin and a bed to sleep on. It is even better to purchase the tickets in the morning or a day before departure as these are popular. If you are a budget traveler that does not mind sleeping in airplane-like seats, you can just take the 2nd class seats.
– A lot of sellers will come by and shout names of products or food they are selling until midnight. Keep this in mind if you are a light sleeper or bring ear plugs.
– Other passengers could possibly leave their windows open in the evening and at night. This can make it chilly in the train as winds come in and can be cold (especially when it is raining!). The cooling fans will also stay on during the fan, not helping the situation. Bring a blanket!
– Mosquitoes. As mentioned, the windows could be open for a long time and it is easy for mosquitoes to come in while the train is standing still. Wear long clothes, bring a blanket and mosquito repellent.
The toilets are okay, but some can be very nasty and smell very bad. A tip is to bring your own toilet paper or napkins as there are no in the train.
* currency at the time of traveling