Compulsive Grocery Shopping

I've devised a theory.

Everyone must have 1 item that they purchase at the grocery store every time they go grocery shopping. Whether the item is needed or not, the purchaser assumes that it is needed because they either a) simply can't remember if there is any at home or b) it's something that is not used very often, but is indeed a useful item.

Mine item is Butter. Or Margarine. It depends on my mood. But for some reason I always think we're out. I come home with another 4 count box of butter and realize as I'm putting it in the fridge that we still have a whole box left over from my last trip. We really don't use that much butter, so why do I always think we're out?

What is your item?

Talk to me.