The 1-st class carriages are more comfortable but less popular because of the price (a 1-st class ticket is about 3 times more expensive than a 2-nd class tickets). First class compartments have 2 beds, an air conditioning system and additional services are available.
If there is no 1-st class carriage in the train, some travelers buy a full 2-nd class cabin, and occupy full compartment. Otherwise, three other people will be traveling with you, which may be uncomfortable and tiring. The cost of a whole 2-nd class cabin is close to the cost of one 1-st class ticket.
Men and women travel all together in Ukrainian passenger trains; the tickets are sold for men and women. This may sound strange for a foreigner, but this is a tradition in Ukraine and other FSU (Former Soviet Union) countries.
Toilets are not separated, either. There are two toilet compartments in the ends of each carriage. During the trip, they may be locked by porters for short periods, when the train arrives to a station.
One more peculiarity - there are no carriages for smokers or non-smokers. Those who would like to smoke, can go to the very end of the carriage, and have a cigarette in a small compartment there.
According to Soviet time tradition, Ukrainians prefer to bring their own foods to the train. Porters serve only tea (coffee) and chocolate bars or biscuits.
If you have no food with you, you may want to experience going to a train restaurant carriage. Most of the trains have such a carriage, usually located in the middle of the train, between carriages 9 and 10. They serve meat and fish courses there, alcoholic and non-alcoholic drinks, and sandwiches.