Select an Activity, right click, and select Duplicate....

Enter a name for the new Activity.

The newly duplicated Activity will appear in the Performance Explorer. It will have the same properties as the Activity it was duplicated from and will start in the new state.
If you wish to change the Activity's properties before running it then right click it and select Configure Options.
Duplicating a Session will not copy any Activities it contains.
Select a Session, right click, and select Duplicate.

Enter a name for the new Session.

The newly duplicated Session will appear in the Performance Explorer. It will have the same properties as the Session it was duplicated from.
If you wish to change the Session's properties then right click it and select Configure.