I'll admit that I don't pay attention, I just buy what I need when I need it. I think I'm the odd one out though. My family is me, DH, DD 7, Dtwins 4, and I watch my cousins three kids during the week. We also regularly contribute snacks to the twins preschool classrooms.
I buy what we need when we need it. Some weeks I might spend $300 but then not really need anything but milk, eggs and bread for a week and a half.
I think part of my problem of nailing down a budget is that we shop in so many places. Milk and eggs come from a farm. In the summer we buy ice cream there too and if we need honey that also comes from there. When they have yogurt we will buy that there as well. It's more expensive than the grocery store but there's nothing weird in it and it's fresh and out of this world taste wise. DH and I literally fought over the last raspberry yogurt
I buy bulk stuff like tp, flour, sugar, cheeses, silk soymilk (for our lactose intolerant family members), etc... at BJ's.
We like Trader Joe's but it is about 20-25 minutes away depending on traffic so we probably only go there once a month, but when we do go we have two carts full. We get coffee and snacky stuff and also a lot of gluten free stuff there.
We like Whole Foods too, again, great for the food allergy/gluten free stuff, but a bit of a hike so we only go maybe once a month or so.
In the summer we like to go to farmers markets and next summer I intend to buy a lot more and freeze it or can it while it's in season. It'll cost more up front but when I'm pulling out cheap frozen in the summer blueberries in winter instead of buying expensive imported ones, it will be worth it.
I think it would probably be easier to keep track of if we just shopped at one conventional grocery store and that was it but with all the food allergies and intolerances, this is what works for us, even if it is a PITA sometimes.
The biggest things I do to save some money are to shop in bulk for things we use a lot of, make as much as possible from scratch (safer with the food allergies too!), and when I catch a good sale I stock up. The flip side of stocking up is making sure you purge the freezer and shelves once in a while because it's not a savings if you throw away a ton of out of date stuff.
Oh and we try to make a menu and stick to it to avoid eating out. The key for us is to be realistic about our schedules. If I watch the extra kids for 10 1/2 hours and then have to chauffer kids to ballet and stuff, as much as it may sound good, I will not be making a gourmet meal. Grilled cheese and soup night is much more feasible on a crazy day. I know it sounds really obvious but setting realistic goals has made a big difference between actually sticking to it and saying the heck with it, let's go out