We've had money stolen from purses but never lost anything from our pouches. When you sleep on the trains be sure to secure your packs to the overhead carriers in the compartments. We carry a little chain to link things together, or we re-hook our shoulder straps around the carrier. These are just to cause a little fuss if someone is trying to take them. When you're fast asleep after a long day of walking you're not going to be too easily awakened.
Theft is common on some night trains and the thieves are very professional.
If you're lucky enough to have a compartment to yourselves be especially alert, the more people in a compartment the more difficult it is for thieves. If you think this has happened be doubly careful. You can get the information on how to order one from a travel agency. You might make up a list of night trips that give you time to get a good sleep. When you get off in the morning you can tour that day and then retrace the route that night.