Doing some at some snooping of how others are using your computer?
There is a log and it is rather easy to find. If you go to applications->utilities->console. Once there you can see a log list on the left side and then under log files there should be system.log
once you found that you need to look for the transfer time. I will warn it does not keep a log for eternity. I find the easiest way of looking for the event your looking for is do a search for "/Volume". Every time that comes up should be an event with the description of "getting new uuid:"
now you have a time an external drive was plugged in. Next, get rid of the search criteria and go to that time to see the logs after it. Then in the system log any events after that that are labeled "Exited: Terminated" in the log will mark a transfer of a file. I dont how, if you can, to pull the name of the file