Getting an accurate idea of grocery spending

Trying to get a snapshot of our budget at any given moment has been a challenge, to say the least. I use MS Money to manage my accounts and I can generate a report, but there have been so many unusual scenarios over the past several months that I am having difficulty determining what we are actually spending on groceries. For instance:

We decided to use some of our economic incentive rebate to stockpile some food items, mainly grass-fed beef. So those are actually grocery costs for more than this month, and I have no idea how long a 1/4 side of beef will last us.

Feeding an extra adult in our home has not really impacted our bottom line...or has it? He contributes $100 a month for food, but his renal diet also requires me to purchase specialty items like rice milk (which is pricey), but something I would not normally buy.

Theoretically, I am feeding five adults (myself, my husband, my teenage daughter, my father-in-law, and my 12 year old son who eats double portions of meat) and one child, a vegetarian. That means I am also buying some specialty items for my 7 year old to ensure that he gets enough protein and B12*.

*I also include all supplemental and vitamin items as a grocery cost: cod liver oil, vitamin C, fiber supplements and multivitamins. I don't practice overkill on the vitamins and supplements, because we do eat a very balanced diet. I order from iHerb, which keeps the costs way down. What we do take in the way of supplements actually helps to reduce expenditures in other areas, such as healthcare and prescriptions.

It appears as though I am spending an average of $125-135 per week on groceries, but I'm not sure if that is an accurate picture, or if I am spending less. With my personality, I have a need to know :)