Put that thumb drive of yours to good use ESPECIALLY BEFORE BRINGING YOUR LAPTOP TO THE HELP-DESK! You should ALWAYS back up your important files before leaving your laptop since the help-desk is not responsible for any loss files. An average sized thumb-drive (4 Gigs- $14.99 at the SU bookstore or 8 Gigs @$24.99) should be plenty of room to copy over all your documents and external hard-drives are perfect for those audio and video files.
Backing up your Mac Files;
Insert the thumb-drive or external in one of the Mac USB ports.
Open the Mac Finder app. (by default the 1st icon on the bottom left of your toolbar)
Drag your Documents folder (under Places) to the drive (top under Devices)
Make sure to drag over any additional folders or files you may have saved to the desktop or folders other than Documents.
Backing up Windows Files;
Same process as above except right-click your start button and select Explore. Go to Desktop>My Documents and drag the ones you wish to backup to your USB drive (Under My Computer). Again make sure to drag over any additional folders or files you may have saved to the desktop or other folders.