I love the Salomon [Salomon XA 10 10][1] I have for this since it comes with a hydration bladder which is removable. When I'm using it for carrying a post-race change of clothes, I either take the bladder out or leave it empty to be filled at the race. When I just want a hydration pack, it is small and light enough to be good for that. For me, this pack was a good balance between being able to carry a change of clothes and having a hydration pack.pack. [1]: http://www.salomon.com/us/product/xa-10-3-exp-set-m.html

I love the Salomon XA 10 I have for this since it comes with a hydration bladder which is removable. When I'm using it for carrying a post-race change of clothes, I either take the bladder out or leave it empty to be filled at the race. When I just want a hydration pack, it is small and light enough to be good for that. For me, this pack was a good balance between being able to carry a change of clothes and having a hydration pack.