Try the SpecOps HUMP. I think that is what they call it: H-harness, and hydropack carrier. I'm not fond of hydrobladders, myself, but the pouch is big enough for something like rain gear and a sweatshirt.
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-IronRaven

When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.