BYOTP does NOT mean bring your own tent; however, no trip to Russia is complete without having some experience riding the Russian railways. Whether it's an overnighter from Moscow to Kazan or Yoshkar-Ola or a multi-day trip on the Trans-Siberian Railway or Trans-Mongolian Railway, one thing you certainly need to bring along is toilet paper. Russians are not known for being hardy merely because of the harsh winter weather, but also their ability to endure toilet paper that feels more like sandpaper than it does like toilet paper.
You should make sure you have an adequate supply for length of your train trip. It might also be advisable to have some supply for your stay in Russia, because my experience has been that you can't always easily find toilet paper in the supermarket either. I had to buy a roll of paper towels and cut it in half the last time I tried to find toilet paper in a Russian supermarket in Yoshkar-Ola.