We're used to spending a lot on food because we're not in the city. In BC, if you're in the lower mainland or Victoria, the Chinese groceries are the way to go for cheap produce. But if you hunt around, you can also do very well at farm gates, rather than at the farmer's market. Talk to the farmers and find out who farms with organic methods but isn't certified--much cheaper.
We have a few ways to keep costs down: the garden and a few chickens for produce and eggs, buying meat in bulk from farmers (1/2 pig, etc); we buy salmon in large quantities in season to freeze for the winter. Lastly, I'm finding out that our local organic co-op has amazing prices if you buy in bulk: at grocery stores, organic rolled oats go for 39-49 cents/100g; if I buy a 22kg bag at the co-op, it's 30cents/100g! Depending on your location, it's worth doing some digging. I also think that CSAs and getting together with others for bulk buys are worth doing depending on your situation.
We're trying to stay out of grocery stores as much as possible, but for things like milk, cheese, etc that are harder to avoid running out for, we watch for sales and use Costco too. Figure out what your real staples are and make sure you're getting the best price. So Superstore/Loblaws is $1 cheaper on our soymilk brand here, Costco is the only place we buy cheese. Our bulk cereal is $10/bag normally, but we know it goes on sale for $6 periodically, and we'll buy a case when it does. Keeping the freezer and pantry full and heading into stores only when we need something specific has kept the impulse purchases WAY down--that might have been the biggest difference!
It sounds like a lot of effort, but we're spending so little time actually shopping, it isn't really! :)