I'm on a train to Vienna and I forgot the documents home, what can I do now?

Milan and Vienna are both inside the Schengen area, so there will be no routine travel document checks when the train crosses the Itailan-Austrian border.

(I'm assuming the passport/ID is all you have forgotten; if you have also forgotten your train ticket, you'll be in trouble, of course).

In principle you're supposed to have documentation with you when you travel in another Schengen country. In practice it is unlikely anyone will demand to see it.

Getting on the flight back to Italy might be a bigger problem -- namely as far as convincing the airline that you're the person whose name your ticket is for. There's a fair chance that your driving license will be accepted for that, but in the worst case it is possible that you'll be denied boarding and have to take a train back instead.

Thanks for all the good answers, it was hard to accept just one.

I'd like to report my experience, it could hopefully help someone else in the future.

Train Part

Despite the announcement of incoming passport and ticket checks, only the ticket has been checked so I managed to reach Vienna without problems.

Airport Part

At this point I was quite scared I couldn't do anything to avoid passport/ID check at the airport so I tried to contact the Italian embassy in Vienna, which was closed. I went to the central police station and they told me they couldn't do anything because my ID hasn't been stolen but I simply "lost it" (that's what I told them in order to get some kind of temporary ID or something). I then tried to call germanwings in order to see if there was something I could do but they simply told me I would not be able to fly.

So, as Relaxed suggested, I tried my luck. I checked-in online and I went through the security check and the gates of two airports (Vienna and Bonn) without anyone asking me for documents.

Have the details with you. The police will be happy if you can tell them your name, address, ID number and some other personal information that helps them identify you. Not having an ID is only an issue when you are crossing the border. If they ask you in Vienna, when hanging around, it should not be an issue. If you are obviously European, then the Austrian police will also get less interested in you. Always be prepared to colaborate to let them check your identity. Do not offer lots of explanations or get cocky. Cooperate. Don't know how they will treat you if you are Somali tough.

Pre-Schengen, I have twice or so traveled with Germans who forgot their passports. Even without a driver's license, but traveling in the same car/bus as family or classmates, they were able to obtain a replacement document on the border -- without a photo, valid for a few days. On a train this is probably not possible, but if you go to the Italian embassy saying you only realised your problem after reaching Austria, they may be able to help you in a similar way.

That said, depending on various factors it's quite possible that you will encounter a routine passport control on your train even though that's not supposed to happen according to official Schengen rules. In that case your driver's license may save you, but really all bets are off except it's a sure bet that your chances will depend on details of your appearance including your complexion, hairstyle, clothing, accent etc. So it's not clear that you will make it to Vienna. You might actually be stopped after the border. There is a chance that showing your flight ticket home might help.