I'm in a strange position here, as I don't HAVE to cook for myself nine months out of the year. But I like cooking. And we can afford it. Being vegetarian at home really helps here, because I know that meat is where a lot of our friends spend a lot of their money, and it just doesn't figure for us.
2) Shop smart. I know which of our four local grocery chains has the best price on vegetables, so I always go there for the veg. Then to another place for the dairy. And another for the cleaning supplies. I used to worry about the gas costs adding up, but all the stores are within a mile of each other, so I'm not worrying anymore. (Plus, I have a Prius: 50mpg!)
3) Limit the impulse-purchases. Don't buy any cool ingredients unless you know how you're going to cook them.
4) Don't be a slave to the list. If dates are cheaper than figs, and can be used in the same recipe, go ahead and make the swap. This really helps me out with expensive ingredients like nuts.
5) Plan ahead. Don't buy so much food you can't cook it up and eat it before it goes bad.
6) If you see inexpensive stuff that your family loves, go ahead and buy it (in moderate quantities.) And drop something roughly equivalent, but pricier, off your list. (Thus: bought two melons because they were cheap and smelled good, didn't buy the wicked-expensive grapes.)
7) If you have storage space and facilities, buy in bulk and store things. We don't have a very big freezer so I don't actually do very much of this, but it's a nice idea.
8) Make your own... bread, cookies, waffles, pancakes, pizza, marmalade, jam... actually, I'm not sure the marmalade came out any cheaper than buying a nice jar at the store, but I know we save lots of money on the other items.
9) Grate/chop/clean your own stuff. I've wasted a lot of money over the years on pre-washed lettuce, baby carrots, shredded cheese, and "ready to steam" broccoli. When I was short on time, I felt it was worth the extra cost... now I don't.
10) Farmer's market/CSA/farm stand/U-Pick... for me, this revelation came last fall, when the local farm stand had butternut squash for 1/5 the price of the supermarket. I couldn't take full advantage of the bounty, as I didn't have a reliable way to store them, but I bought five and we ate them over the next month.