Like I added in my edit, there is almost no such case: Sundays are a mandatory day off for most. That means you can't go shopping on a Sunday, except in very few shops (train station shops have exceptions). Doctors, pharmacies and most other emergency things operate on a reduced schedule.

I'm not certain what would happen if say a nurse working a shift in an ICU was selected. I'm pretty sure it's either announced early enough that the hospital would have to switch shiftees or they would be given a pass for free. I suspect a person working in a train station shop on a Sunday would tell their boss, and would simply be shifted to another time (it's not like the boss or the employee can do anything about it - it's law).

EDIT: to clarify once again - I'm pretty sure it does happen, but the case is probably rare enough for it not to matter too much. The rule works for a good 90% of cases, exceptions can certainly be done on a case-by-case basis at community level.