Doplním, že s rýchlovlakmi a Interrailom je to otázne:

"Reservations on the TGV high-speed trains are compulsory. We recommend you make your reservations as far in advance as possible.

Please note that international TGV trains offer a limited number of seats for Interrail pass holders. Once these seats are taken you will need to purchase a full-fare ticket. We advise you to reserve the trains as far in advance as possible. You can start making reservations up to 3 months in advance."
https://www.interrail.eu/en/plan-your-trip/trains-europe/high-speed-trains/tgv