there's the more typical copy/paste..
edit -> copy (ctrl C)
edit -> paste (ctrl V)
you can also paste in place .. edit -> paste in place ... which will let you copy items from one SU window and paste it in the same exact place in another window.
or select some geometry you'd like to keep, then ctrl C, then delete everything you want gone.. paste in place and the stuff you want returns to it's proper place.
[i think the menu is called 'edit' on PC.. if not. ?]