Do you expect to also tour with this bicycle or is the primary use in getting groceries?
The reason I'm asking is depending on that answer another alternative might be a trailer like a Burley Travoy. I have one that I use as a grocery cart and can even wheel it inside the grocery store with me. I also have racks and panniers but find the Travoy a little more handy for my grocery runs. On the other hand, I wouldn't want to tour much with the Travoy.
As far as wheels go, it depends a bit on what wheels are currently on the bike. If it is a reasonable touring wheel/hub, I'd be inclined to wait until it comes time to replace it before proactively getting new wheels.