Mostly it's bread as the only consistent item.
It's not weekly either, it fluctuates when we do grocery shopping.
We do meal planning and figure out what meals we need and shop based on that. Onions, pasta sauce, different varieties of pasta, meat, pork chops, milk, etc all vary on when they get bought. We buy half gallon milk as when we used to buy gallon milk too much too often would go to waste.