This is one of those Photoshop tips that you’ll either use all the time or never.

Press Command-Option-Shift-E (PC: Ctrl-Alt-Shift-E) to Stamp Visible layers, which creates a new layer on top of all the visible layers below. This is really useful when you want to apply a filter to the compiled image but want to keep all of your existing layers intact. The only downside is that it can increase the file size dramatically.