hi just to share. I have an Osprey atmos 35 and I am very thankful for it for a few reasons.
one is that because i travel alone most of the time, i don't like to check my luggage in, so this backpack is really good coz from outside it looks small enough to carry on the plane, and it is the biggest sized backpack that can fit in the overhead compartment.
two is that you can squeeze ALOT of things in there. I have traveled with this backpack to Thailand (1-2weeks x 8-9 times), Japan (10 days x 2), China (1 month), HongKong (still here) and so far from tiger airways to ANA to SQ to China southern airlines to jetstar to airasia, I have no problems bringing this subtle monster up. I always subtly worry they will force me to check in coz i pack in sometimes up to 30kg worth of stuff but friends opinion is that it doesn't look that big and heavy.
So when i travel i have a sling bag (terrclime 100) that i put either my netbook (asus 900) or my dslr (450d) along with my travel documents, mp3 player, bible, notebook and pen (all essential carry alongs that i require). So if i hve both my cam and netbook i put the either on in the bag and carry/sling the other. Why netbook out is because at security checks you have to take it out anyway, so you would want to lessen the hassle. And with that out of the bag i plonk everything in m pockets in teh bag, so i can walk through the detector with no hassle.
anyway back to your concern of hostel. I face the same problem, so what i do if i do not have safe is to bring along all my valuables in my sling bag and with the cam round my neck and valuables in the bag i make my way around. This is assuming you only bring 1 lens around, if you have more then you could get bigger sling bag to accomodate what you want to bring along.
the net is actually something I am considering too!
well, this is my view and I hope it helps! really, though a bigger can fit more, the hassle of waiting and all is not worth it in my opinion and in reality, you would rewear some of your clothes just because 'it doesn't smell'. But given the constraints, and the situations, backpacking is not a fashion show, and if you are willing to explore and rough it out, you just need a strong spirit and a really good cologne/ body spray! ;p
happy travelling!
