Create a new PST on the flash drive (File>New>Outlook Data File),
right-click the calendar folder you wish to copy, and choose Copy.  Specify
the flash drive PST as the destination.  When the copy completes, close the
PST on the flash-drive (i.e., right-click its root and choose Close) and
exit Outlook.  You can now dismount the flash drive and restart Outlook.
Take the flash drive to the system which is to receive the calendar, insert
it, open Outlook, and open the PST on the flash drive with File>Open>Outlook
Data File.  Copy the contents of the calendar folder to your main calendar
there, close the flash drive PST the way you did before, and close Outlook.