Is it just the two of you? No kids?
It depends, of course, as to how you shop, and for what.
Do you cook from scratch, or buy a lot of prepared meals to warm up, etc?
Do you buy much produce, as this can be pricey?
Do you smoke?
My wife and I (we live in Canada) spend on average about $50-60 per week, but we don't buy steaks, and cuts like that, due to the cost.
My wife cooks from scratch, most times.
So, $120 per week sounds a bit high.
The other thing to ask is, do you buy all your household stuff in a grocery store, or do you shop in other places? Items like toilet paper and paper towels, cleaners, we buy from Wal-Mart, not our grocery store. So, if we combined our grocery and Wal-Mart bills, it would be much closer to yours.