Toting grocery bags is good for our muscles to a certain extent, but overburdening them can bring on days of relentless pain. I still drive and still tote groceries every day from the neighbourhood stores, but only one or two bags (I have the monthly grocery supply delivered to my house). I find it's good exercise, even though I do walk a bit like a drunk whenever I carry more weight on one side than the other.
All in all, I try to remain active and lately, since the days are longer, we have added a short evening walk around the neighbourhood, because it really makes a difference in my sleep quality.