How can I merge layers, but not lose them in the process?

By the experts at Adobe. © 2005 Adobe Systems Incorporated.

You can merge layers in Adobe® Photoshop® CS2 without losing them in the process by stamping them. Stamping allows you to merge the contents of more than one layer into a target layer while leaving the other layers intact. Typically, the selected layer is stamped down to the layer below it.

To stamp multiple selected layers or linked layers, first select the layers. Next, press Ctrl+Alt+E (Windows) or Command+Option+E (Mac OS). Photoshop creates a new layer containing the merged content.