What is a good going away gift (for PCS/PCA/retirement/separation/ect.)?

As I have looked back over the "brass and glass" collected over a career, all, without a doubt, are greatly appreciated. But I've found over the years the ones that have meant the most to me, and caused me to think back about the great times, are the ones that have incorporated a photo of people I worked with. Over the years, seeing those faces of people I've been through both good and difficult times with triggers much deeper feelings and recollections than the ones without pictures. But as I said, they are all appreciated.

I'm a big fan of Guidons, Snowshoes, NCO/Officer Swords (the real ones, not the fake sabers you see all the time), KA-Bars, Shadow Boxes, etc... Basically wall hangers...

I dare you to give him/her an old toilet seat for the field, then watch as they laugh. Then bring out the real gift.