As others have said, maybe share your itinerary, or at least what countries you will be travelling in. Your biggest issue will be countries and trains that require reservations, where you will need to pay an additional fee or may find limited availability, or may not be of much use, like the "chunnel" train.
If you are feeling concerned based on the previous comments, keep in mind that usually, by taking slower regional or intercity trains in some cases, you can still get where you are going with no additional cost.