I've got the Topeak Explorer rack on several bikes. I love the track system for use with a trunk bag.

However, for groceries I use panniers, so any rack would work for those. I tried a few different ones, and settled on a few of the Arkel bags. Very fast one-handed installation and removal (you literally just lift by the handle and it detaches) and you don't need to use any attachment at the bottom of the bag... they just attach at the top. Most models come with the usual hook for the bottom, but you don't need them, and I removed them from the bag that had them. Even without the bottom hooks, they are the most secure bags I've used, about the same as Ortlieb bags.

The Shopper is cavernous, and easy to fill at the store. It also carries around easily. I've had other panniers that were better for commuting or light touring, but for shopping, this one is the best by far that I've used.

https://www.arkel-od.com/en/shopper-foldable.html