Lowepro Photo Trekker AW II Camera Backpack
This is the biggest of my fleet of camera backpacks. I carry it locally when I need 5+ lenses. I’ve also taken it internationally a few times, including a backpacking/Eurail trip across Europe. Traveling, I was able to pack everything I needed in addition to camera gear and carry it all comfortably, thanks to the AWII’s highly-adjustable back and straps.
One of the nice features for travel is the secondary daypack that piggy-backs to the back of the main pack. You can drop off the big pack in the hotel room and detach the daypack with ease. The whole pack is carry-on-friendly for airliners also.