Short notice on Sapsan fast train and a link where you can book and buy Sapsan tickets yourself.
In general in Russia: train tickets are available for purchasing 45 days before the trip date the earliest.
1st class: including hot meal according to the menu, fresh tea, natural coffee, non-alcoholic and alcoholic drinks
2nd class: no meal, no drinks included
Seats and cars are the same for both of the classes. You will have the same experience and the same comfort in both of the them.