Hydration system

It's no longer convenient for me to plan my long runs around water sources, so I'm thinking about carrying water with me. I'm currently doing 14 miles for my long run but hope to work my way up to a marathon this spring. Could some other runners give me advice about a hydration pack or belt you have found to be helpful? (or ones to avoid)
Some features I am looking for are:
- comfort (of course), so no bouncing, rubbing, not too heavy
- enough water for marathon training
- at least 1 small pocket to carry food

I don't have strong feelings one way or another about a belt vs. backpack but am more concerned with overall comfort for a long run.

Thanks!

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