Last year I got a pair of Arkel Utility Baskets...these are no longer on their web site but it looks like the City Baskets have taken their place. These are basically one big pocket that you can dump a lot of stuff in. 3,300 cubic inches for the pair. Pretty waterproof, with built-in waterproof hoods (on last year's model, anyway) and optional rain covers. These aren't even on Arkel's Touring web page, but worth a look if you want to load up with food and water and not have to hit the stores so frequently.

Arkel - City Basket - Perfect Commuting pannier