I've 4 kids and spend between $250-$275/week on groceries (this includes household supplies, but not gas). I've also been trying to stock up my pantry when things are on sale, so I have been buying a little more than what I will use in a week.
I also typically save $15- $30/week in coupons (most of them are from the Sunday paper- i usually get at least 2). I often manage to combine coupons and sales, and get things for next to nothing- sometimes even free. I do really well with toiletries that way. I usually get Colgate or Crest toothpaste, for example, for anywhere between 29 cents and nothing :)
I try to make a meal plan for the week when I find out what meats are on sale. This time of year, I tend to spend more because I buy more fresh produce and more meat (DH is a grilling fanatic-lol). The other seasons, I make soup once a week (cheap) and we tend to have more frozen veggies (all purchased on sale) so I save quite a bit there.
Do you have a membership to a Sam's Club, Costco, or BJ's? We have a membership to BJ's, but the closest one to us is about an hour away, so we only go once a month or every other month. They are finally building one closer to us though, and it should be opening this fall. We save quite a bit there though, especially when we use the coupons they send us in the mail.
Good luck :)