The last couple years I have been travelling with the Osprey kestrel 38L backpack. It is a really well built bag and has always packed enough for any length of travel. I like the sleek design, boot compartment on the bottom, ventilated back piece and compression straps.
This year I am using the 25L Pelican U160 Camera Backpack. This is the most bad ass bag I have ever uncounted. This bag works really well for me as it only allots about half of its space to photo gear, which can be hard to find in a camera bag. It gives me just enough room for my camera gear, 11″ tablet, clothes and toiletries.