Merge All Layers to New Layer
IF you have Photoshop document with lots of layers or multiple layers, you may come to the stage where you need to merge all of these layers into one layer, while you still want to retaining your original layer structure. Well since there is no menu feature to do this in Photoshop, however there is a hidden hotkey. Cmd/Ctrl + Shift + Alt/Opt + E.
This will combine everything and pop it onto a new layer in one fell swoop.
and you are done.