TIP: Copy all visible layers

Normally, if you Select All and Copy, you will copy the contents of the one active layer (the one you have clicked on in the Layers palette). If you want to copy the contents of all visible layers - without flattened - try this: after showing the layers you want to copy, press Command Option C (PC: Control Alt C) and Photoshop will copy a "merged" version of the visible layers (the command is actually called Copy Merged).