The first and foremost thing that you need to take with you on your trip documents and money - it is the most important in the journey. It is better to have a small bag or backpack that you always carry and take in your hand Luggage when flying.
So, what to take with you on vacation:
Passport and copies of them. Generally, copies of all documents have phone, flash drive, cloud storage/virtual drive or email - but better to be safe and to choose several options. These copies may be needed if the originals are lost.
Print and electronic options for reservation of hotels/apartments.
Print and electronic versions of tickets.
Print and electronic versions of insurance.
Credit cards (better to have multiple cards and accounts of different banks).
Small format notebook with his records and notes, a pen and a pencil. It can be used for communication and bargaining.
The Phrase Book.
Download to your mobile phone or tablet programs with offline maps. Find out what else mobile apps can be useful in the journey.
An international driving permit if you are going to rent a car.