Very interesting reading.
So, the things that I take away from this thread:
1) Make no assumptions about the condition or contents of a cache. Use appropriate caution before/when opening one.
2) People who find a cache (especially non-geocachers who accidentally stumble across it) are not always prepared to leave something, so they are apt to leave whatever they happen to have in their pockets/purse/pack. The interesting thing is that such people apparently DO feel compelled to trade rather than just ransack the cache or even just put it back untouched. Ammo, keys, various personal products all fall into the category of "something I just happened to be carrying that amuse me to leave behind".
3) One man's trash is another man's or child's treasure. A significant portion of this thread (when it's not about dead bodies of various sorts) is about finding "junk" and wondering why it was left. The answer could well be that a parent was humoring a child (the parent whose youngster liked to leave golf balls or the child with a toy dinosaur, for instance) and that the "junk" was not considered to be trash by the one who left it. The lesson would seem to be that while there IS a line between honest to goodness garbage and real swag, that setting an artificial bar in your mind for what constitutes "acceptable" or "appropriate" swag may just be a way of reducing your own enjoyment of the outing instead of appreciating whatever story may exist behind an odd piece of "junk". In the instance of parents allowing children to leave tokens, it might be useful to note in the log that "my five-year-old hopes someone has fun with the army man" or some such.