Choosing the BACKPACK:
As I did not have a backpack I started researching what to buy. Most of the backpackers recommend the front opening backpacks as it is more convenient to search what you need in the backpack without taking everything out (versus the open top ones).There are a lot of reviews you can find on Google about the different types with advantages and disadvantages for different types, I won't list any links here on that as it depends more on everybody's priorities.
I decided for Osprey Farpoint 55 simply because it is a 2 in 1 backpack. It's a 55L backpack having actually two parts. A 40L (37L for S version) + 15L Daypack. I did manage to get it as hand luggage on Iberia, but it is a fine line, make sure you don't over load it and that you wear it as 2 separate pieces. No guarantees though especially if flight is full.
I bought mine from Amazon.de for aprox 153 Euro (February 2015)
What to Pack: