On brevets with controls about every 50 miles; food and water is always available at controls, I use an Ortlieb large saddle back and two 1-liter water bottles, Zefal magnums - Amazon has them. I use a 2-liter Camelbak for hot rides where 50 miles with 2 liters won't be enough. In that case, I also carry 1 or 2 of the Zefals. My Camelbak is minimal, with water only. A Camelbak improves aero, the main reason they are not legal for racing.
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Results matter