The fact that you mention renting cars and staying in hostels, and you plan to backpack four different countries in just two weeks, suggests you have not looked closely at this website. The kind of backpacking we do around here involves walking trails to get from one place to another, carrying all our food, water gear and clothes with us, sleeping in tents, and generally hanging out in places cars would be of no use because there are no roads.

I'm moving your inquiry to the off-topic forum because some of our members also backpack in the way you wish to and someone might be able to offer the sort of the advice you're seeking. Have fun on your trip!