I use front ortlieb panniers for small grocery trips. For a larger load of groceries I prefer a cargo trailer (mine is a Croozer I bought five years ago for $150). I find this easier to manage. I can easily get bigger loads and bulky stuff (try packing a case of wine and a big box of laundry detergent into your panniers along with fresh produce/other supplies).
It's particularly quick to load and unload. At the grocery store I just transfer my bags to the trailer. There's no distributing of the load into multiple panniers and sorting out what goes where. At home I wheel the trailer into my kitchen and unload it - which is easier than if I came home in a car and had to shuttle bags from the car to inside the house.