In trying to reduce file size for PSD, does eliminating saved selections do anything? I've found lots of useful tips, but none relating to selections. Thanks.
If I remember well, each type of layer can each easily add an extra 20mb+ to your unflatten .psd file at high resolution.
If you're using the same mask for many layers, you can group these layers in the same folder and use the mask on the folder instead.
But since you don't want to remove your selections or layers, there is something else you might want to try and that can help reduce the file size.
In Photoshop, all the layers that are not showing on your artboard are still "hidden" in the gray area around your design. If you imported big images that go off the working area, they are still calculated as pixels in your document and they add up to the weight of your file.
If you don't mind losing that kind of data, you can crop your psd file or erase these unused parts to get rid of that "dead weight". It's not always the ideal solution, but you can do some clean-up there on some layers.