For the benefit of anyone who may search this topic in the future, I will follow up on my own thread and perhaps close it out.

Further online research revealed that there is nothing, or next to nothing, of a retail nature that is open in Levallois after about 13.00 on a Sunday. Therefore, I modified my plan. I found a Monoprix with a good wine selection just a few hundred metres from Opéra so I took the Roissybus from CDG. Then, after making my purchase, I took the #3 metro directly from Opéra to Levallois. Yes, the bus is slower than RER>4>3 but I was not in a hurry so I traded time for convenience.

All's well that ends well.