In reply to Imedio:
You could get something in the larger size alpine packs say 45-55l which will be featured and probably big enough for multi day gear with a lightweight rack and rope. You would need to be seriously smart with packing technique though. As others have said, the moment you include an overnight stay, bags will fill very quickly, with the exception of bivvying or by having super lightweight gear.
Also, unless its a bag that can be stripped down significantly and compressible, I would imagine it would be a pain to climb with if you plan to do anything multi-pitch.
I would suggest you get a decent sized trekking bag that is comfortable with heavy loads. You can load up it up with the necessary gear, without being too conservative and then throw in a lightweight daysack. That way you are not limited by how much you can carry and can mooch off on your adventures with a dedicated climbing bag that is suited for purpose, whilst leaving the rest of your gear at base. If you plan to relocate your camp, then its just to pack everything back into your trekking bag and off you go in relative comfort. If you're only doing a daytrip then you just take the daybag.
I use the Cierzo 28 or Alpha FL 45 depending on season, when doing weekend long trips that also include (normally multi-pitch) climbing. They weigh next to nothing, take up almost no space in the pack and add a massive amount of flexibility.