Trans-Siberian Train

Get enough food and water to get you going but you can buy most things you need on the station platforms along the way. You don't have to rely on horrible packet soup. There's lots of othr interesting stuff. Vodka is cheap and fun to share but buy a name you know or get a friendly Russian to help you as the really cheap stuff can kill!
Get some plastic clips that can close food packaging which will be useful anywhere.
Bring some soap in a dispenser to wash your hands in the bathroom.
Bring some salt or condiments along as well as a spoon.
Remember all trains in Russia run on Moscow time so ideally have a watch that stays on Moscow time so you can plan for the stops and when you have to get off.