Actually, you don't have to bring much more than some money. The best thing to do is do go on a Transsib journey in a group of 4 people. You can try more things, you have you "own" and relatively big compartment to retreat (usually there are 9 compartments per car), you can still get easily into contact with others, and you can always taste some of the things other travellers "obtained" at the platforms.
Practical add-ons to your luggage are 3- or 4-flange keys, which - if necessary - can open a bathroom door (these will be closed during 30 minutes before and after the stops as well as for a few hours at the borders) or which will allow you to pull down a window for a short time until the Provodnitsa will realize it and probably scold you. WWW.BAIKALINFO.COM
Practical Hints for Your Time Aboard
Actually, you don't have to bring much more than some money. The best thing to do is do go on a Transsib journey in a group of 4 people. You can try more things, you have you "own" and relatively big compartment to retreat (usually there are 9 compartments per car), you can still get easily into contact with others, and you can always taste some of the things other travellers "obtained" at the platforms.
Practical add-ons to your luggage are 3- or 4-flange keys, which - if necessary - can open a bathroom door (these will be closed during 30 minutes before and after the stops as well as for a few hours at the borders) or which will allow you to pull down a window for a short time until the Provodnitsa will realize it and probably scold you. 
Important things are cup, plate, cutlery (spoon, knife, fork), and can opener. The cup is good for showering, having some tea, and drinking some vodka (do better not use a plastic cup). Small souvenirs such as postcards of your homeland, coins, sweets (Ferrero chocolate products are considered a delicacy in Russia) and other small things are wise things to bring. However, the times when stickers and ballpoint pens were causing joy are over.
In case of snoring compartment members or excessive sensibility when it comes to rail clattering you should bring ear plugs with you.
A small pillow, pajamas, towel, a book, slippers, and a camera with many films will round off the feeling of comfort.
Should you happen to travel with an organized group these hints are also important. Individual travellers are recommended to stop by at the car of a travel organizer, since there you'll be most likely to find up-to-date information on the landscape passing by on the walls of the car (the best information can be found at Studiosus and DER-Tour travel groups).
Sometimes - on friendly request and if the Provodnitsa happens to be a little inattentive - you might also be able to shower there because travel groups are usually placed in First-Class 2-bed compartments.
The trains also have a baggage car where bulky luggage or bikes and similar things will be stored in exchange for cash. Even the dining car might be turned into a baggage car if necessary.