Manfrotto Offroad 30 L could work well for you, it has the biggest bag-pack-compartement for non-photo-gear as far as I know: https://www.manfrotto.com/products/camera-bags/camera-backpacks/off_road and it is very light.
The LowePro Flipside Trek 350 or 450 are the most advanced products (and as far as I know the newest) camera-backpacks with non-camara-compartements: http://store.lowepro.com/flipside-trek-bp-450-aw what I realy like is the opening-mechanism, you twist it and open it from the rear side without removing it from your body or have to lay it on the floor. And it's also a good protection from pickpockets ......
The 350 you could take into an airplane, the 450 is a little (!) bit too big.
And I'm afraid that if there would be a backpack with either
- more camera-space, than it would not have enogh place for non-camera-stuff
- more space for cloth etc. than it would have less space for camera gear
- more space for both, camera-gear and non-camera-things than it would be much bigger and too heavy that you want to carry it, and the backbag itself becomes heavier and heavier ..
So I think one of the above mentioned could work well ....
The LowePro Flipside Trek 350 or 450 are the most advanced products (and as far as I know the newest) camera-backpacks with non-camara-compartements: http://store.lowepro.com/flipside-trek-bp-450-aw what I realy like is the opening-mechanism, you twist it and open it from the rear side without removing it from your body or have to lay it on the floor. And it's also a good protection from pickpockets ......
The 350 you could take into an airplane, the 450 is a little (!) bit too big.
And I'm afraid that if there would be a backpack with either
- more camera-space, than it would not have enogh place for non-camera-stuff
- more space for cloth etc. than it would have less space for camera gear
- more space for both, camera-gear and non-camera-things than it would be much bigger and too heavy that you want to carry it, and the backbag itself becomes heavier and heavier ..
So I think one of the above mentioned could work well ....