On Web, you can duplicate lists and tasks. On Windows, you can duplicate lists but not tasks.
Basically you can have templates for lists and duplicate them on both Windows and Web.
An error occurred while saving the commentMike commented
Workaround on OSX:
1) Select to print list
2) In dialog to print, in the bottom right is a PDF drop down
3) Select "Open In Preview"
4) Select the list and copy from Preview
It is annoying that a standard UX behavior is not supported. It's more annoying that you got rid of a perfectly good application, Wunderlist, and decided to replace it with one that does not support this standard UX behavior. You should have left Wunderlist functioning until To Do was fully functional.