I have a Mountain Hardwear 30 litre pack that weighs 720g and is waterproof. It is great for a light pack, but has horrible water bottle compartments - which kills it.
I think the Osprey Talon pack (with an added splash cover) is about the best balance you’ll find. It is very comfortable, and has pockets on the hip. With a splash cover, it weighs about 1kg, and is 33 litres. I have done 3 of my Drakensberg Grand Traverses with that pack.
My Hi-Tec Cedar 45 litre pack (which has done 2 DGT’s, although it was being used by my team mate) - and it is also a great light weight pack for a very reasonable price. The Osprey pack is better, but it does cost almost four times as much. The pack above is more expensive than both.