Documents :

Passport/ID:

Passport validity:

Foreigners wishing to enter Turkey should carry a travel document (passport) with an expiration date at least 60 days beyond the “duration of stay” of their visa, e-Visa, visa exemption, or residence permit.
Further information and exceptions you can find here: http://www.mfa.gov.tr/general-information-about-turkish-visas.en.mfa
Passport/ID validity is very important, we have already seen people denied to enter the country due to expired passports!

Visa legislation:

The best and most up to date information you'll find at the website of The Ministry Of Foreign Affairs of Turkey: 
http://www.mfa.gov.tr/visa-information-for-foreigners.en.mfa

Countries whose citizens are allowed to enter Turkey with their national ID’s  for a stay of 90 days:

1. Germany
2. Belgium
3. France
4. Georgia
5. The Netherlands
6. Spain
7. Switzerland
8. Italy
9. Turkish Republic of Northern Cyprus
10. Liechtenstein
11. Luxemburg
12. Malta
13. Portugal
14. Ukraine
15. Greece

Online Visa:

All citizens of other counties can apply for online visa here: https://www.evisa.gov.tr/en/

Driving license:

A national driving license is enough!
A driving license for motorbikes is necessary for renting a bike.

Health insurance card:

Must be valid for foreign countries! Ask for the Asian part of Turkey also.
If possible, private hospitals should also (or especially) be covered
 

Travel insurance:

Watch out for cover of private hospitals and transportation back home! Watch out for clauses excluding certain countries (Turkey) or certain activities (motor biking, rafting,...)

Deposit:

Traveller cheques / credit card or 500.- Euro/Dollar in cash, as a deposit for the bike rental.

Money for the shared cash-box:

During the tour you will need approx. 300 Euros for fuel and beverages (depending on your thirst!) We will collect this money on the first day for a shared cash-box. Changing money outside Turkey usually means a low exchange rate, so it's best simply to bring Euros.