A couple of points from my experience, although these are hardly new insights:

1. Even if you buy the ticket at the machine just before getting on the train, you need to get it validated/stamped. I knew something about this but not how seriously they take it. On my second train trip, the conductor came through and told me that my ticket was not valid and I needed to pay something absurd like 40 or 50 euros (for an airport to town ticket that cost maybe 8 euros). I showed him that I only had 25 euros in my wallet. He took 15 or 20 euros. The other trick is to find out where this validation machine is....
2. I rented a car in Italy. When I returned the car in Switzerland, they said that there was damage although I was not involved in any accident; I suppose it was pre existing damage which I didn't see, especially in a very dark garage where I picked up the car. I had gotten some extra insurance from Hertz so I thought that would cover me. Otherwise, I have coverage from my credit card, and from my regular US auto insurance (I might had something else as well, but can't recall offhand). It turns out that the insurance from Hertz didn't cover the first 2000 euros of collision and all other insurance coverages (such as credit card and US auto insurance) don't cover rentals in Italy (and a few other countries in the world).