One of the strangest features of the Eurail Pass is that they force everyone over the age of 26 into First Class. This doesn’t appear to be a problem! (Although you may be able to make your journey’s more cheaply by buying second-class point-to-point tickets.)
Here’s our experience of complementary nuts and cookies as we travelled from Bern to Berlin, reaching speeds of around 250km/hour, on an ICE train.
Reservations on Bern-Berlin are recommended but not compulsory if you take this route during the day (I’m not sure about at night). We choose a time we thought wouldn’t be busy and had no problems finding seats. In fact, we had a whole six-seater cabin to ourselves for 90% of the train trip.