As a rule, shops are not open on Sundays in Switzerland (like other European countries). Some exceptions are the ShopVille at the HB (where you can get food if you forget to plan ahead) and some restaurants.
This time of year are three other exceptions in Zürich. It’s so amazing that they even had to call it Sunday Shopping rather than Verkaufsoffener Sonntag or something. Five other cities have also adopted this experience, and that information is here.
Not all stores are open (our favorite toy store was not open last Sunday, but will be on the 21st). We saw a child crying near the store, and we surmised that the closure was the reason for her tears.
Tomorrow the city gets a Sunday day of rest from this extravaganza (last week we bumped into throngs of people downtown), but not to worry, glampers. You still have next week to look forward to!