In reply to ballsac:
I have the gourdon 20l with the side pockets for water bottles & its ace, however for multi day hiking trips I find it a tad small with my 250g summer weight down bag inside plus other items.
For my recent camino de santiago hiking trip, I used a OMM classic 32 which was brilliant - much more durable than it looks and much more comfortable than the gourdon. Also the large mesh pocket is ideal for stowing wet clothes to allow them to dry.
gourdon has the advantage of being half the price however. As others have mentioned, the decathlon bags also look great for the £££ and I saw a large number of people using these on the camino.