– Books (when your child has other kids around, they are willing to play with each other rather than reading books on vacation).
If you travel even in May to the South of Italy, take with you warm socks and pyjamas for night sleep.
If your kid is under 4 years, take a lot of extra clothes for him/her. Because of rains or humidity, the clothes you wash may dry a very long time.
You should control the number of toys your kid will take with him/her.
Be ready to offer several snacks for your child to eat in plane, airport transfer or train.