Window shopping at the über-expensive stores; there are also tons of Souvenir shops;
FAO Schwartz had a flagship store there (I saw that they’ve closed the one in Manhattan, so I’m not sure about it);
Go up the Üetliberg for a great view of the lake and city… when there is time, it’s a nice day hike, but you can get there by car, and I recall busses going up there also;
If the Üetliberg is not an option, there are dining boats that ride around the lake; that’s a good way to see some scenery as well.
Get dessert at Sprüngli;
Those are the things I remember most about Zürich… I was born there (43 years ago on Wednesday; I don’t remember that!), and visited there several times over the years, but I’ve not been back in a decade.
I think if I went back, I’d like to explore the architecture more… There are some amazing old cathedrals and such.
Do you have any hobbies or particular interests? My Uncle arrived from Switzerland last night. I could ask him for more suggestions.