I spend about $75 a week for groceries for an eight person household. Here's how I do it:
1. One bean/legume based dinner per week and one egg or cheese dinner. I also do one pasta based meal. We only eat red meat on Sundays.
2. Eat only in season. It worked for our ancestors.
3. On the odd occasion that I have an extra piece of meat, I make a big pot of soup with it.
4. Figure out what staples are dirt cheap in your area and eat primarily those. Here, I can get pasta for .50/lb at the dollar store, rice for .25/lb at an ethnic market. Guess which two grains make up the bulk of our meals.
5. Avoid anything in a box or plastic bag. Good for the budget and the waistline. On the rare occasion that I'm not pregnant, I run about a size 6 without putting too much effort into it.
6. Buy loss leaders and only loss leaders. Buy a lot, enough to last you until the next time they are a loss leader. I buy cases of $1 jars of pasta and $1 boxes of cereal at Albertsons and leave without looking in any other aisle.
7. Do not go back to the store, no matter what. You will stop forgetting as often if you subconsciously know this is your only chance.
8. Be careful with beverages. I get coffee free-have a stepson who works at Starbucks. We only buy soda when it is obscenely cheap and drink tea or water otherwise.
9. It usually isn't meals that kill a grocery budget, it's snacks. So watch the snacks. Buy a huge bag of apples or oranges and let those be the snacks. Make homemade muffins, homemade cookies, homemade bread, etc to fill everyone's carb cravings.
hth!