Lake cruise! Lake cruise! I think it takes one or two hours and you get to see fantastic views. Also, if you are in a hurry, you can get out at the last stop and take the much faster train back.
Also, yes to buying chocolate but let me try to remember the name of the shop that sells artisan chocolate near the shopping area. It may be closed on Sunday.
Public transportation in Zurich is amazing. Buy a day-pass.
no time, flight boarding in 30 minutes.