Here are some tricks for working with layers in Photoshop CS6 if the Layers palette gets too crowded and you want to: apply the same filter to multiple layers; streamline your Layers palette; or work with multiple layers as a single entity:

To: Do:
Merge the active layer into the layer below Command+E/Ctrl+E
Merge all visible layers into the active layer Command+Shift+E/Ctrl+Shift+E
Merge a copy of all visible layers into a new layer Command+Shift+Option+E/Ctrl+Shift+Alt+E