if you are looking for a pack for ultra trail races, 2 lbs is insanely heavy. you want something under 1 lb.
Nathan HPL 20 is probably the most popular among racers, but there are others.
It has a bladder, but does not hold very much else, since its for racing.
Even for general trail running, you can do a lot better than a 2 lb pack.
Heck, you're only going to have 3-6 lbs of stuff in it.
If you want a pack that is more for hiking but for some casual running, the Black Diamond Bbee is a great simple pack. weighs 13oz.
Black Diamond Bbee