I'm glad this was a learning experience for you Badger. I often have the opportunity to pack out others trash as well. I hope your friend has a chance to return the cache. As far as the "tracking device" my guess, as I have heard of this happening before, is that someone found the cache and either dropped or forgot their GPS device near the site. The next cacher that went to the site prolly found it and placed it in the box in case the original owner might be back to look for it. The find of the device may have even been logged in the journal.
There is a neat ammo box cache along the hike to Whale Peak above Gibson Lake. It is filled with whale themed items. Searchers are able to leave items at any cache box.
