I could use a cutbrush, but I'd like to register everything perfectly and it's hard not to be a pixel or two off with the cutbrush after a couple espressos

I tried copy/swap spare, and image menu copy image/paste to new layer, but all I end up with is a copy of what's on the current layer and not everything visible. Also tried "new layer from current image" but that just gives me a new blank layer? What's the difference between layer and image? Image sounds like it would be everything visible but it's not.
I found a horrible hack way to do it (Merge all, copy to spare, undo, new layer, swap spare) but there's got to be an easier way.