thousands.

The one I have as my profile pic is my first and only challenge coin so far, but I'll be getting me quite a collection soon :P
It's a duplicate of the one I gave to my fiancée. Very simple front, but the bak is engraved with "hold this in your hand while I hold you in my heart - forever and a day"
We have a long distance relationship (even now before I leave for basic) and we both do coin checks with each other where we carry them around everywhere and text each other pictures of us holding them.

I've got a few. The two I treasure most are;

The first one I received back in 1995, from a US Army SF A-Team we worked with,

And the one I received from the CO of a USAF AeroMedical Evac squadron that I (and my team) provided close protection to in Iraq in 2005.