Great question, Kysaroko! I have been a mom for 16 years, and I have changed many things over the years, through trial and error. Here is what is currently working for our large, one-income family.
I do a meal plan for a month, with input from everyone, and post it on the fridge (no more "What's for dinner?" questions allowed...read the list!). I usually do 2 weekly menus and alternate them, meaning weeks 1 and 3 of the month are identical, and weeks 2 and 4 are identical. THis helps greatly with making my shopping list, and allows me to buy lots in bulk and use it up over the month. This has also taken out the stress of wondering what to make for dinner tonight!
I do at least one night a week with a crockpot meal, or something that just simmers on the stove all day, like chili or meatballs and sauce.
I try to do a wide variety of fruits and veggies over the course of the week. We usually do fruit at breakfast/lunch and then salad and veggies at dinner. My kids will eat almost anything if they put ranch dip on it, but their favorite is carrots. Hubby is a big carnivore, so there is always meat at dinner.
My oldest son has Type I (juvenile) diabetes, which means his pancreas no longer makes insulin and he is on an insulin pump 24/7. Since he was diagnosed 2 years ago, we have been doing lower carb meals, with very little bread/pasta. Recently we went gluten-free, so if we do eat bread/pasta it is gluten free. The GF thing has caused my grocery bill to go up quite a bit :(
I try to not buy packaged items like juice boxes, water bottles, snack bags, etc because they are more expensive. I buy big bags of tortilla chips and gluten-free pretzels when on sale. We drink mostly water or fresh-brewed tea at home, very little juice and no soda or soft drinks. We use refillable water bottles when we go out.
In terms of cooking, Hubby makes breakfast on Sat/Sun, and my 3 oldest kids make one meal per week, usually lunch. The rest is all me! But I don't mind cooking...it's more fun than cleaning and laundry for sure :)
As for cost, I would say I spend an average of $300 per week between grocery store and Costco, which adds up to a little over $1200 per month. It is higher since going GF, but that's only been one month and I haven't added up the difference yet. But I figure $133 per person for a whole month is not too bad. If I use coupons and shop REALLY carefully (like in a month with other big expenses...think BRACES here) I can keep it to $1000.
Looking forward to reading other people's responses to this question!