Do I need to book big or heavy luggage separately?

It is not possible to travel with big or heavy luggage other than a suitcase or a rucksack. So, sledges or other big (sports) articles are not allowed on the train. A pair of skis or a snowboard are allowed. You may also bring a folding bike, or a bike packed in a bag that is no larger than a suitcase. Make sure that the skis, snowboard or folding bike are stored where they will not inconvenience other passengers. Check with the train crew. Incidentally, you don't need to book a suitcase, rucksack or pair of skis/snowboard separately. Remember that the train crew may refuse your luggage if you do bring oversized luggage with you.