From my own experience - In no Particular order;
1) Rick Steves - Europe Through The Back - Travel Skills Handbook (37th Edition)
Take this book or read it carefully before voyage.
2) Europe by Eurail 2018 (2018 Edition)
3) The "ROUGH GUIDE" - Europe On A Budget (March 2017 publication)
4) Arthur Frommer's Guide To Europe (2017 publication
What are some of your books That you take with