Tom Nelson told me in Catechism class that somewhere in Europe (probably in the 50's) the pharmacies would be open on Sunday, but only the back of the store where the prescription drugs were dispensed. The rest of the store (toys, soda fountain, household goods) would be closed.
This brings up an interesting point though. MORE people lived in the country back then. But it wasn't necessary to shop on Sunday while "in town for Mass" for several reasons:
1. Mega grocery stores or supermarkets didn't exist yet. Every small town had a grocery store, and it didn't cost an arm & a leg more to buy your monthly groceries there compared with the local supermarket.
1A. More people lived in the country, and produced at least a % of their own food. In particular, those things that don't keep for long (fresh ingredients for home cooking). It's easy to keep stocked up on canned goods and non-perishables. What sends you to the store often are those fresh vegetables you need to make this or that dish.
1B. Things were more local than national, and certainly not global yet. There were a lot more viable "local" and small, family owned businesses.
2. This was before the Crisis in the Church, and the "1+ hour trip to Mass" became a fixture or a given for all serious Catholics. Your trip to Mass on Sunday was a trip the closest Catholic Church!
3. Money was worth more (heck, our coins were still 90% silver as recently as 1964) so there was much less necessity for husbands to work 2 jobs, wives to work, or families to be extremely frugal (on gas, time) just to survive. It was a different world back then.
4. People had family they could hang out with on Sunday. Today, people are spread out all over the country, often extremely isolated from family and/or other Trad Catholics. Also, even when family is technically present, they are so different from a Catholic mentality that it is difficult to spend much time with them. This might not apply to you, you might think it sounds far-fetched or crazy. Trust me, it isn't. It's all too real a situation for many good Traditional Catholics. Remove too many things they "can" do on Sunday, and they'd start dreading the Lord's Day as being a day spent in a prison cell where they can't do anything.
"The Sabbath was made for man, and not man for the Sabbath." -Our Lord
Long story short, God will understand. Just be honest with yourself, honest with God, and do what your conscience tells you is right. Everyone knows if they're properly dedicating Sunday to God, or if they are cheating. It's the spirit of the law that really matters. Quibbling about how many miles you can travel on foot on the Sabbath (the Pharisees worked this one out. answer: 2 miles) or how many mouse-clicks constitute servile work is something for Pharisees -- not Trad Catholics.