We will be travelling from Paris to Bayeaux (and back), Paris to Dijon (one-way), Aix-de-Provence to Monaco (one-way) and from Monaco to Pisa (one-way) by train in late June and early July. Do we need to buy our train tickets ahead of time, or will it be possible to simply show up at the stations and purchase the tickets. In other words, to train seats in France and Italy "sell-out" in the summer and/or will be get a better deal purchasing in advance? Thanks in advance!
Tickets almost never sell out on most European trains (except some night trains) BUT you might be able to get a discount by booking early.
An exception might be TGV trains on a Friday (or other pre-holiday) afternoon in the summer. We travelled from Paris to Avignon by TGV the last Friday in June 2007 and about every five minutes in the Gare de Lyon was the announcement that all the trains to the south of France were full and that everyone should take the train they had a ticket and/or reservation for.